Although just included as a fun minigame, I though it would be nice to expand on the Pet Battles by adding some more useful and vanity items to the game. Some of these I see as rare rewards or drops and some I think could be created by players. (the crafting ideas build on an earlier idea of mine).
Reply with your own suggestions. If you like any of these hopefully Blizzard will look at add them in future content updates.
Rewards or Looted items
Tiny Skull of Power - when this item is in your inventory, all Undead pets gain extra experience in battles.
[achievement x] - you can summon an additional companion outside of a pet battle (you can have 2 summoned companions)
[achievement y] - you can summon an 2 additional companions outside of a pet battle (you can have 3 summoned companions)
Tiny rain cloud - a new battle pet. This companion looks like a small black cloud that flys after you. It randomly rains (or even shoots lightning bolts on occasion)
Birdcaller - when used this summons up to 15 random flying pets from your journal which whirl in a small cyclone about the spot.
Silver lining - when you have this item in your inventory, you earn extra reward for any Battle in which you had an Elemental pet in your team
Feel the Magic - when you have this item in your inventory, whenever you summon any Magic type pet, it will appear in a random effect; appearing through a portal, phasing in, appearing in a flash of light, puff of smoke etc.
Buggles - target player sees all other companions (and critters) as cockroaches while the effect lasts
Player Crafted Items
[First Aid] Emergency pet bandage - restores 20% of pet health, usable in combat, once per combat only (not pvp battles)
[First Aid] Field pet bandage - revives and heals 1 pet fully (not usable in combat)
[Alchemy] Potion of the little game hunter - increases your chance of finding better quality pets (lasts 30 minutes)
[Alchemy] On Safari potion- reduces cool down of Pet Heal by 2 minutes (lasts 30 minutes)
[Tailoring] Zookeeper's sack - holds all pet items (including caged / unlearned pets)
[Blacksmithing] Reinforced cage - reduces damage taken when casting cage by 10% (lasts 30 minutes)
[Blacksmithing] Spiked collar - pets do 3% more damage (lasts 10 minutes)
[Engineering] Mechanical trap - increases capture chance by 5% (lasts 30 minutes)
[Engineering] Collapsable podium - summons a small, winners podium which your current team mounts, and then emotes from (last 3 minutes, 8 hour cool down)
[Inscription] Writ of challenge - allows you to challenge a trainer (once per day, in addition to normal daily)
[Inscription] Spilt ink - pet leaves dirty footprints after it as it follows you (lasts 30 minutes)
[Jewel crafting] Gemmed collar - pet leaves sparkle trail in the air after it as it moves (lasts 30 minutes)
[Jewel crafting] Loyal companion for life - creates a life size, stone statue of your pet (lasts 3 minutes)
[Enchanting] Twisting Nether challenge shard - initiating a battle transports you to a random location for the duration of the battle (ie. random background for your battle, each battle uses 1 charge)
[Enchanting] Windfury scroll - pets gain 3% speed (lasts 10 minutes)
[Leatherworking] Barding - pets take 3% less damage (lasts 10 minutes)
[Leatherworking] Lucky animal foot - increases your Luck in battles (lasts 10 minutes)
Differing levels of the above could apply to different zones/expansions.
Cage / Trap Buffs do not stack. Buffs to speed, damage, toughness, and luck do not stack.