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.
This cards is made using the Baby Whips Technique (Making your own pad with baby wipes and reinkers. The butterfly is from Butterfly Basics and cut out using the Butterflies Thinlits Dies and the Big Shot