Item Mastery Feats or 'How to pull off being a dime store wizard'

The fireball exploded across the pier and set more of it on fire. 

"Running out of pier aren't we?" Callic yelled over the roar of the growing flames. Kess glared at her friend as she looked around the massive stack of tea chests they were hiding behind as the sorcerer was joyously blasting the docks in an attempt to kill them before they could get away. 

"You know nagging me won't hurry this along." She growled back at her friend as she pulled the book mark out of her journal, pulling at the ambient energy out of it and pointing a hand at the flying man approaching them. 

One moment the man was cackling as he hovered forty feet over the burning barge of fuel oil, the next a look of shock came over his face as he dropped like a rock into the roaring blaze with a shriek. 

"Boom.." Kess said with a smirk just before the barge blew up and shook the entire ward.

Explanation: Magic Item Mastery feats are feats that let you use the latent magic of magic items to cast spells one or more times a day. Now there are a few requirements: specific base Fortitude Save* and a specific rank in Use Magic Device.  

As per Weapon Master's Handbook, Pg 26:

Item Mastery Feats

Using an item mastery feat is a standard action that doesn't provoke attacks of opportunity, similar to activating a command word item, though you do not need to speak to use the feat. Creating these effects requires you to assault the existing magic of the item through your force of will and channel the item's inherent magic through your own body; this act is thus governed by the user's fortitude. All effects created by item mastery feats act as spell-like abilities and use your base attack bonus as the caster level. Any spell-like ability's save DC is equal to 10 + the spell level + your Constitution modifier. If a spell-like ability calls for a calculation using your Intelligence, Wisdom, or Charisma bonus or modifier, use your Constitution bonus or modifier instead.

Magic item mastery is stressful for the item as well as the user and can't be performed on items that can be used only a limited number of times or that must be recharged (such as elixirs, potions, scrolls, staffs, and wands)—it requires items with constant effects or daily uses. Magic item mastery doesn't affect an item's normal properties or deplete any of its daily uses. The following magic item mastery feats are available to any character who qualifies. 

What this can do for a character is open up a lot of new and interesting abilities that could help in a variety of ways. One or two feats gives you a bit extra utility in your day to day actions or a handful to make you more of an unusual character than the average guy (or gal)

Now, two or three classes REALLY stand out in one away or another. Fighters are among the best with a good base Fort save and copious feats to pay the 'tax' of feats to spell like abilities. Other martial types are good on the Fort save side of things with fewer feats to contribute to the selection of abilities. 

Item Mastery Feats: 

• Ability Mastery (MTT): Preqs: UMD 3 Ranks, +4 Base Fort Save, item with transmutation spell of 2nd level+. If you're on a tight budget and need a +2 enhancement bonus to a stat as long as you have armor or a wondrous item with a transmutation effect of 2nd level or higher. To set up things you have to focus for 10 minutes and then for the next 24 hours you get a bonus to a stat of your choice. Good if you are a particular build that doesn't need a high bonus in a single stat, say a +2 to dex, while wearing your Belt of Physical Might +2/4/6 (Str/Con), or adding a +2 to your will save or buffing up Int/Cha for a particular skill.
• Compulsion Mastery (WHB): Preqs: UMD 3 ranks, +6 Base Fort Save, item with enchantment spell of 3rd level+. You can cast suggestion once a day, plus once more @ +9 and +12. Now at first glance it's not a good one, but it might be useful if you're subtle or clever. Not one of the big 'got to' ones in my opinion. 
• Concealment Mastery  (MTT): Preqs: Stealth 3 ranks, UMD 3 ranks, +3 Base Fort Save, item with illusion spell of 1st+ level.  This one is a two tier feat. If you go with just a 1st level spell, you get vanish but if you get one with a 2nd or higher illusion spell and have +7 ranks of Stealth and UMD, you get access to invisibility or undetectable alignment. Either level is very useful and you get an extra use @ +9 and +12 Base fort.
• Curative Mastery (HH): Preqs: UMD 1 ranks, +2 Base Fort Save, item with a conjuration spell of 1st level or higher. This is a prime one, you get to cast a healing spell. It can either scale up, each additional use bumping the cure light wound up a step till you hit breath of life at 5 uses, gaining one @ +4/6/8/10/12 Base fort save. One of the better ones, if simply for the convince of being able to heal yourself or others. NOTE: This feat uses the caster level of the ITEM and is an exception to the BAB as Caster Level. 
• Curse Mastery (WHB): Preqs: UMD 3 ranks, +6 Base Fort Save, item with a necromancy spell of 3rd level +. This one is pretty nasty, in that you can cast bestow curse on someone. A 6 point reduction of a stat, -4 to attack, saves, ability checks, and skill checks or a 50% chance to do nothing each round are all nasty options. Add in another use @+9 and +12 Base Fort
• Dispel Mastery (WHB): Preqs: UMD 3 ranks, +6 Base Fort Save, item with an adjuration spell of 2nd level+. This is another very useful one in that you can cast dispel magic thru your item. Dispelling spells on your foes, or if you feel gutsy, applying dispel magic as a counter spell. With some extra spells @+9 and +12 Base Fort 
• Energy Mastery (WHB): Preqs: UMD 1 rank, +4 Base Fort Save, item with 1st level+ evocation of acid/cold/electricity/fire descriptor. A 1st level spell lets you cast burning hands (same elemental effect as the item being used), for 2 daily uses you can cast a lightning bolt of the same elemental effect. Additional uses come @+6/8/10 and 12 Base Fort. Very useful for groups and or ranged attacks of an elemental type.
• Flight Mastery (WHB): Preqs: UMD 3 ranks, +6 Base Fort Save, item with 2nd level + transmutation spell. Without a doubt one of the most effective feats, who can't find a situation where having the ability to cast fly isn't helpful? Additional castings @ +9 and +12 base Fort.
• Force Shield Mastery (MTT): Preqs: UMD 3 ranks, +3 Base Fort Save, item with an abjuration 1st level+. This enables you to cast a magical effect similar to shield, but the actual AC shield bonus is based on 1/3rd of your base Fort save, with additional uses @ +6/9 and 12 base fort.
• Illusion Mastery (WHB): Preqs: UMD 2 ranks, +4 Base Fort Save, item with an illusion spell of 1st level+. This allows you to cast minor image, with an additional casting of +6/8/10 and 12  base Fort. Minor image is one of those spells that requires some consideration before using it. Throwing up a wall, shifting the door a foot to the right; it's all about being subtle in using minor image.
• Implement Mastery (MTT): Not an actual Item Mastery feat per se, but the main reason that an Occultist character is an awesome choice for an Item Mastery PC. You can use focus points (half as many as the required Fort Save bonus) to activate the feat, which can easily offset the Fort save/usage issue of some of the feats. 
• Racial Item Mastery (MTT): Preqs: UMD 6 ranks, +3 Base Fort Save,  item associated with your race that grants a spell like ability. This one is WAY conditional. I can not think of many items that are applicable. Most likely candidate for this sort of item would be planar half-breeds (Aasimar, Tiefling, etc) or the Kitsune. You can get an additional use @ +9 and +12. I wouldn't suggest this unless you have a power/ability from your race that you want to use more times a day. 
• Resistance Mastery (MTT): Preqs: UMD 3 ranks, +3 Base Fort Save, item with an abjuration spell of 2nd level +. This is another excellent utility feat. You can add +1 resistance bonus or 5 points of energy resistance against one energy type for 24 hours. Like Ability mastery, it's one you can tune at the beginning of the day. 
• Restoration Mastery (MTT): Preqs: Heal 5 ranks, UMD 5 ranks, +3 Base Fort Save, item with a conjuration (healing) 2nd+ in it. At the base level, this allows you to cast lesser restoration; a higher investment of Heal and UMD of 9 ranks and a conjuration (healing) of 3rd level or higher opens up the ability to cast either remove blindness/deafness or remove paralysis as well. Additional uses coming @ +9 and +12 Fort save. This one is another useful but conditional one. 
• Symbolic Mastery (MTT): Preqs: UMD 4 ranks, +2 Base Fort Save, holy symbol of the god you worship. This one is fun in that you can literally unleash a bolt of power thru the holy symbol of your god; blasting foes with the power of your faith with a ray of holy (or unholy) power that can be untyped, positive/negative energy or elemental power (depending on the domains your god offers. It's one of the most potent ones as you can unleash a number of blasts equal to your base fortitude save. So a fighter could throw up his shield, complete with the symbol of his/her god on it, and blast their foes. Very nice image eh?  
• Telekinetic Mastery (WHB): UMD 5 ranks, +7 Base Fort Save, item with a transmutation spell of 4th level+. This allows you to cast telekinesis and while not the best of spells in combat, it does have its uses: sustained force, combat maneuvers or a violet thrust. It's bit wide in it's utility as can be seen, with an additional use @+ 9 and +11 base fort. 
• Teleportation Mastery (WHB): UMD 4 ranks, +6 Base Fort Save, item with a conjuration spell of 3rd+ in it. This one is fun as it allows you to cast dimension door, which makes it right up there with Flight Mastery for sheer utility. On the battlefield it's an awesome utility item. Additional uses come +9 and +12 base fort. Note: theoretically this could allow for access to the dimensional dervish feat chain. 
• Vision Mastery (WHB): UMD 2 ranks, +4 Base Fort Save, item with a divination spell of 1st level+. This one is one of the more useful utility feats, with the ability to cast either dark vision or see invisibility. Amazing utility for a non-caster with the ability to get an additional uses @ base fort save of +6/8/10 and 12.
• Weapon Evoker Mastery (MTT): UMD 2 ranks, +3 Base Fort Save, weapon with a special ability to do energy damage (acid, cold, electricity, fire or sonic). Simply adds and additional 1d4 damage of the same type each time you hit that round. It's a swift action to activate and mostly is 'meh'. 

Relevant Classes & Archetypes

Fighter: Mixing in a high base Fort save and copious amounts of feats to balance out the loss of effective 

- Relic Master (WHB)

Occultist: Without a doubt a very topical choice for an Item Mastery PC. Add in the Implement Mastery feat and the ability to use focus points to augment uses/day. Not to mention a class built around pulling ambient power from props just screams item mastery as a feat chain. The ability to build up UMD ranks is a bit easier than a fighter but your base Fort save will slow down the extent of use, but focus points can easily over come that.

Notes & References: 

HH: Healer's Handbook

MTT: Melee Tactics Toolbox

WHB: Weapon Master's Handbook