The general idea is to spruce the crag up by replacing the old belay stakes with shiny new ones, remove some trees in the base of the quarry, give any routes that need it a good clean.
Climbers wanting to help out should bring the usual gear for these sorts of events plus any sledgehammers/posting hammers they might have for getting the stakes in.
Generally, the usual gear means gloves, old clothes, gardening tools, patio knives and brushes.
Also, a harness, helmet and all the safetly gear imaginable is useful if you are abbing routes to clean them. Rope protectors are handy too. The BMC will provide the cakes, in the time honoured fashion that we do. Lemon drizzle anyone?