I'm not big on giving gift cards. I know that people like them, but I don't see it being much different than cash and find it rather impersonal.

Flowers with a note. A local florist might can put together a special price for multiple arrangements to the same address.

A food, candy, or fruit basket can be nice, affordable, creative, and durable for travel. Especially nice if you put one together yourself with items that are unique to your own hometown.

Also, a positive note to their supervisors is always appreciated.