Felt Owl Crafts - i should make one of these for every single one of my students! they'd really remember me (well mostly my crazy owl classroom!) You could glue the felt, or use the patterns with paper
Balloon Rockets - I've done this in several science camps I've conducted. Kids have fun with it. But, when the balloon deflates it may fall off the straw because it's surface area changes - another good thing to show and explain to kids.