In reply to 7bforever:
There's a campsite called Outdoor Alternative at Rhoscolyn. It's private and you need to ring and arrange to camp before you arrive.
And for North/South Stack we always used to stay at the Valley of the Rocks site. Not perfect but cheap and cheerful. There's a pub/bar adjacent to it, and I remember seeing a sign saying you could get a pint of Diamond White for a quid. Tells you about the type of pub it is (karaoke every other night, etc)! Never had any issues on the camp site though.