In reply to 98%monkey:
Most walls if they don't know you will want to see a qualification certificate and proof of insurance, although this is to get group entry rate at a wall. Also work to a ratio that the wall allows usually 1 to 8, but when coaching the ratios are often a lot smaller.
Although many walls may have a different policy, usually a quick email/phone call can sort out what needs to be bought along or even sent prior to your visit.
I have only turned up at one wall unexpectedly as the group needed to go to a different wall to work towards there CWA. I had to log into my MT DLog which had my certs and insurance cert. Ironically I was working for a very well known centre on the day.