I like this idea, but would try to extend the water theme. Put plastic fish inside with a gift card to Bass Pro Shops! A gift card to the pool store or local water park would be fun too. I'm all about making the gift card connect.
inspired ideas-Project No. 5 A pretty little paper frock
a collection of hat blocks via stylecourt
Loulouthi dress form -- Urban Outfitters "loulouthi" is greek for "flower"