a few ideas:
1. princess hats (triangle shaped with gauzy material at the tip that flows down the back, the type with the mickey mouse ears attached.
2. get each a t-shirt, then bring a pc. of cardboard and a black laundry marker. you can have characters sign the shirts (my kids REFUSE to get rid of their out grown ones-so get them big enough to be worn for play and as a night shirt). p.s. you can always get these for much less $$$ at the character wherehouse near wdw.
3. a couple of bags of mickey mouse tortilla chips (shaped like mickey's head), my little one took these for snack time at preschool and they were a major hit.
4. autograph books, but take a small, legible, foldable sign.
on the sign write "hi (and then their names), have the characters pose holding the sign, that way you could do double prints and make each of them a personalized book from their friends at wdw.
5. last but not least-the little wind up toys that are available almost everywhere (about $3.00 each) they come in a variety of characters in cars, boats, etc. these last forever and they will play with them endlessly.
p.s.-if you stay on property and buy any of the refillable mugs at the resorts-kids LOVE THESE. we had a pile left from a couple of trips that i was going to toss until everyone let out a roar, so we passed them on to family and friends. (it does bring back memories of trips gone by when i see one of my much older brothers lugging around his coffee in a guady port orleans mug

). the kids drink out of them, use them for water play, and eventualy they end up in the back yard for important excavation work.
have fun shoppin!