You must wake up painfully early. The first cars roll in before sunrise. Bring a torch and a thermos of tea. The fields can be muddy, so old trainers are a must.
Giant Car Boot - The Giant Car Boot
Also, beware of the “tat”—stuff no one wants. Chipped mugs, broken toys, and VHS tapes of soap operas. You’ll see them in every stall. The secret? Ignore them. Hunt the sparkle.