Hey Derby!
I stayed in St Merryn for a boys surf week only last month.
We had a wicked time. In st merryn you've got a couple of good pubs and restuarants, i recommend the cornish arms by the church which is a little away from the the main crossroads but worth the walk. Be warned they do stop serving food a little early, i think about 8.
Theres also a nice restaurant called waves on the higher harlyn campsite and thats ace but you have to book.
Surfwise you've got harlyn which is just up the road and there is loads of free parking too. We didnt surf it that week as it never picked up but i spoke to a local and they said sometimes it does. Oh and you've got constantine too.
Aside from the restaurants above you're gonna have to travel to find much else going on.
Wadebrige isnt far and you can hire bikes and cycle the old tarka trail which is fun or just explore the town... but that wont take long.
Thats about all i can offer Derbs, have fun tho and if you can recommend anything once you get back PM me as i'm back down there in sept
Cheers
soops
PS: just read that back and it doesnt read too well but i'm a bit tired to edit it. apologies
EDIT:
Oh, and there is a mad go kart centre nearby... a friend of mine went there on a stag do a year or so ago. Apparently they are the most powerfull karts in the southwest and he said it was one of the best days out he's had... but you'll have to work out where that is