Must have engineering items?

[Saraki]

I was wondering, what are MUST have engineering items?
I'm intrested in things like: teleports, pets and mounts.

If you have a suggestion, please add a link to wowhead. I'll make a list in my first post.

To start off:
Moll-E

THE list:

Gadgets:
Jeeves
World Enlarger (requires Gnomish Engineering)
Crashin' Thrashin' Robot (fun item but the recipe is a bit rare)
Moll-E (portable mailbox)
Loot-A-Rang (Lazy looting)

Teleports:
Ultrasafe Transporter - Toshley's Station (requires Gnomish Engineering)
Dimensional Ripper - Area 52 (requires Goblin Engineering)
Wormhole Generator: Northrend (gets you around!)

Pets'n'Mounts:
Pet Bombling
Tranquil Mechanical Yeti
Lil' Smoky
Mechanical Squirrel Box
Flying Machine
Turbo-Charged Flying Machine

[Energon]

I find I use this quite a lot to help me get around when Hearth/Tabard is on CD
http://www.wowhead.com/item=48933

A Cata auto corpse looter
http://cata.wowhead.com/item=60854

[Spellweaver]

Gadgets:
Jeeves
World Enlarger (requires Gnomish Engineering)
Crashin' Thrashin' Robot (fun item but the recipe is a bit rare)

Teleports:
Ultrasafe Transporter - Toshley's Station or Dimensional Ripper - Area 52

Pets'n'Mounts:
Pet Bombling
Tranquil Mechanical Yeti
Lil' Smoky
Mechanical Squirrel Box
Flying Machine
Turbo-Charged Flying Machine

[Tholl]

I tend to PvP as much as I can. (World PvP, I can't stand arena).

So I always make sure I have rocket boots, mind control cap, parachute cloak, frost grenades, and either rocket on gloves or haste (Depending on spec. Haste is great for my shockadin).

I also managed to snag a Arcane Bomb shematic from the AH for 50g. (They go for about 20k+).

Pally with a ranged mana burn/grenade dmg that scales with Spell Power @ a 1:1 ration with a 5 second silence? Yes please

[Saraki]

Thanks for the suggestions guys! I'll keep the list updated =) (happy collecting, atleast I'm collecting them =D)

[Onyki]

Also
Gnomish Army Knife
Gnomish Cloaking Device

[Strawberry-cyanide]

Don't forget Critter Enlarger. <3

[BagOfChips]

Wouldn't call a non-combat pet a "must have".

[Breccia]

I still carry the discombobulator ray. 20% movement reduction can be helpful and it seems to work on most targets.