After receiving the cute parcel (thanks again Chloe) a fun idea came to mind.
An all Summer Best Friend Swap Box!
During the Summer you could put some cute things into a box e.g. strange/cool sweets from the country that you're in, funny holiday pics, cute things from the souvenir shop or something Summery that you've made! That way your best friend can have a piece of your Summer and some of your memories. It would be almost as if you spent the whole Summer Together! :)