what's your plan for the summer?

Nothing

Learn to play the ukelele then audition for a cheap reality TV show. Use your new super ukelele powers to win it and become rich.

~ Do voluntary work - either at a charity shop or with an 'after school' type activity (the only one I can think of right now is a dance class).
~ Join a sports group/club - swimming, golf, running, tennis, etc. Or join a leisure centre and use as many facilities as possible.
~ Get a summer job (though I'm pretty sure most companies are sorted by now).
~ Do some babysitting for a family member/friend.
~ Do car washing or something similar for family members/friends.
~ Take up some other sort of group - art/yoga/etc.
~ Go for days out by bus/train.
~ Visit museums/places of interest.
~ Make some sort of art -you can buy them little wooden models, that have loads of individual pieces, and you build it.
~ Redecorate your house/room.

EDIT: You could also:
~ Learn a new instrument.
~ Learn a new language.
~ If you want something mindless - watch old movies/tv series.

I appreciate the work here lol! Rep +1. Already started to hit the gym, and I'm getting back into learning guitar. I think even though I have loads of great mates, after uni, I've gone from lots of social stuff, to like days on end of non-social things. Akon sums it up pretty well.

Ergh.

It seemed pretty much summed up with just that one word, but I thought I'd elaborate a little more.

After finishing my uni exams this summer and going out with mates, is anyone experiencing those days, of just empty a) What to do?! and b) what the hell have I done all day?!

I'm thinking of going all out, and just making a water slide down my stairs, or pm'ing random people with questions like "What's your 4th favourite colour?" and/or the age old favourite of "Can you do a backwards roll?"