Never been to York, but I have been to my fair share of large train meets, including four TCA national conventions. Never really had a large budget though. I would say take half your cash in $100's, 25% in $50's, and the last 25% in $20's, $10 and $5's. Seems like a reasonable mix, while keeping the bulk down.
I don't know if personal checks are accepted the way they used to be. In the old days being a TCA member came with a level of trust, though there were always horror stories of bad checks.
I'm a big fan of credit cards wherever possible, and don't mind paying the fee, unless the deal for cash is exceptional.
