Well, to be honest, it completely depends on what your interests are! What do you enjoy doing? Also - there's nothing wrong with you taking the time this summer to get practising at a sport you think you'd enjoy. What sports take your fancy? Remember that sport takes practice, and the summer will provide with plenty of time to do whatever, y'know? As for other hobbies - well, anything. I found loads of suggestions on google (I would type out suggestions here, but these lists are huuuuge and will probably help much more!):
http://www.listof.org/list-of-hobbies.html
http://en.wikipedia.org/wiki/List_of_hobbies
http://www.listofhobbies.net/
Honestly though, it just depends on what you enjoy doing. And, as I said, if you want to do a sport then there's nothing stopping you! Even if you find it tricky and difficult - practice makes perfect, right?
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the laughter penetrates my silence
as drunken men find flaws in science