Last year we brought this Zinka sunblock and it was a lot of fun... everyone wants to stay protected from the sun and have fun! They don't seem to have any available for prime, but it's worth it.

or you could go for a nighttime fun thing and get some El wire... totally portable and has different flash settings. Just bring extra batteries! They are fun to watch/wear and make you stand out at night with your group so you can find each other better. Just wrap the wire around yourself, your hat, you bag.. whatever and turn it on!