I bagged a bargain at Cash Converters in the winter, a medium fridge that runs off mains or 12v and works a treat. The real benefit of it being "biggggggggggerrrrrrrr than the average !" is that I can pre cool it on the mains at home, add a couple of frozen 2ltr bottles of water and it will remain cold over night without draining the battery. Plug it in the next day and hey presto, does about 5 days before I either buy ice, ready meals, or ask in the supermarket for their waste ice from teh fish display and add in a sealed bag.
I picked up a huge chest Igloo cool box from a boot last week for £3, the bottles of ice have remained frozen for 5 days to date. Of the two options the cool box seems the best in the long run due to the capacity.
Most camp sites do have freezer facilities, but robbing scrotes nick your cool packs, easy if you only use frozen 1,1.5, 2ltr bottles of water as they are free and not worth nicking ! A couple of tackle shops I use will also re freeze my bottles no problem at all, will probably use the cool box for fish & bait and the fridge for food and milk. Be nice to not have mackeral flavoured cornflakes this year ! PMSL