We had O's 5th birthday party (a month early so our friends who are moving to Costa Rica soon could attend), and the "decorate your own cupcake" activity was the highlight of the party! We typically don't have many sugary snacks or snacks with artificial colors in our house, but we broke that rule (big time!) for O's party!
When we went shopping, she chose blue sugar sprinkles, color sprinkles, color marshmallows, jelly beans, chocolate rocks, etc. She used all of these things to decorate her own birthday cake, and then we also used them for the cupcake activity. Fun times!