I usually share a booth (split the rent) and buy fad products to sell at christmastime. Right now I'm selling the worlds only balloon (cant see gift inside) that you can take home and put gifts inside without using any special equipment or skill. Averaging $250 net profit per craft show/flea market day. Granted, I cant sell these 7 days a week, but the extra money adds up. Not all craft shows allow retail goods, but some school/church shows do.
You can also try selling crafts on Ebay At Christmas time. Who knows, you might just double your profits!