I do the same thing for my kids that my parents did for me. They are each allowed to pick out one souvenir for approximately $10-$30. Past souvenirs included stuffed animals, hats, mickey grabber, figurine set, slinky dog toy, and more I'm forgetting. They, and I as a child, have always been happy with this approach. It never even occurred to me to buy more than one souvenir until one of my preschool students returned from Disney with a stuffed animal, shirt, necklace, and more. I have always been satisfied to be on vacation and get one souveneir.