Plenty of old fork-lift pallet,s around. Knock the corner blocks off and lay flat in your boot.Costs nothing to ask and most people are glad to see the back of them.
Thanks for the replies - I'll grab some from b&q - just checking I wasn't missing a bargain that everyone knew about apart from me.
I've not got time for pallets as I'm going tomorrow! I may be able to get a couple from work for the next trip though but I'd have to take all the nails out - I wouldn't want the kids (or any body elses) to get a nail in the foot :-o
The sites we goto don't tend to have any rules (or facilities!) - although it's been 2 years since I've been to this one so I may call to check.