I haven't done a Craft Show in a while, but I totally got one of these, just in case. It's a Credit Card Reader that you use with an App on your smartphone. It seems pretty awesome cause you don't need a merchant account with a third party to accept credit cards on-the-go. There is no monthly fee, just a small % of sales, and the payment is directly deposited into your bank account.
The last craft show we went to, EVERYBODY had one. It's super easy & you don't have to record anyone's credit card #'s, so your customers might be more comfortable with that.
Check it out if you've ever found yourself loosing a sale cause you only take cash.