We usually do a barter table with the kind of idea that, "It's nae loss what a freen' gets", and y'know? it doesn't matter how much stuff I take along to clear out, I always go home with something else that's brilliant/interesting/just what I was looking for

There is also the individual's 'blanket' of set out stuff for sale; usually good kit that's their budget could do with getting a bit of return from....and for the rest of us there's no feeling greedy about buying instead of taking stuff, iimmc
Food wise, we bring our own, but if one eats we should all be able to eat, and we all bring far too much, and the communal meal cooking is a brilliant idea for at least the main meal of the day.
Best advice is that if you know your diet is likely to be different is bring enough specifically for yourself. Otherwise .....well I mind one meet where at the end I had 12 stew packs left to disperse amongst the company, and there must have been 3dz eggs and bacon too. Staples are always good, and you can take them home if they're not used.
For those coming by public transport, don't fret and end up lugging loads, I know you all want to bring stuff to share, but think about the weight and bring just enough. No water on site, so you need to bring that with you. If you have the car handy, then I find a pack of 2lt bottles more useful than one of the huge square waters from the supermarket.
The camping area is 100m or so from what Stuart said earlier, so it's not a burden to carry stuff.
If no one's got a spare flint and steel to barter/sell then contact John Fenna and buy one of his Welsh bushcrafter Dragon's breath kits

or EverythingMac, WhittlerKev or Dave Budd for a steel. There are a lot of really good and highly thought of Makers on the forum, but I have steels from those four so I can personally recommend those people, it's not a snub to anyone else that I do so.
There should be a good selection down at Wooplaw and folks will let you try them
cheers,
M