Rikku's a thief. She can lift an average person's wallet without them realizing it. She can even punch someone and end up with their wallet. If you need something pickpocketed, she's your girl.

She has a set of lockpicks that were given to her by Aly, and she's fast with them.

She's an Alchemist -- she has lots of random items in the leg-pouch of hers, and can mix them up to make a water bomb, a healing potion, a protective shell, or any number of other combinations. A lot of those are explosives, but not all.

Rikku can hold her breath for thirteen minutes underwater. This is a learnable skill, in her canon, and there is an entire sport based around it. Her cousin Yuna back home says "there's a trick to it," and is up to two and a half minutes. She's been teaching Reno; he's up to six and a half.

Rikku has a knack with mechanical items, and likes to take things apart and put them back together.

Rikku can make armor, if you need it, and can also upgrade your current weapon or armor (if you / your canon allows for it) -- i.e., your weapon now has Flamestrike on it, which adds fire damage, and so on. Please note that upgrades are permanent and can't be reversed, and that weapons and armor can only have three or four upgrades, total.