Lots of great input here!!! I also have done craft fairs for about 25 yrs. As some have said, don't expect to be paid for your time. You will find that some things you will make a decent profit on, and others you may wonder why you bothered. My biggest mainstay is a knitted baby "bomber" hat. I KNOW I am not making even 10 cents/hour on these. I don't mind because to me they are "found" money. I never sit without picking up my knitting needles, so time in front of the boob-tube, lunch break at work, etc., the needles are always going. It's amazing how many hats I turn out in a year...and they always sell out!! I rarely bring home more than one or two!!! People keep having babies, and I am now known for these hats, so am sought out. Once you get known, people will look for you and your sales will get better each year.
Another good seller is purses. Most women like to have something a little different....so why not make something different? ;) They make up fairly quickly, and can help to bring people to your booth if you can display an especially attractive one up higher to catch peoples eyes. I make everything from everyday purses to evening bags to beach bags....and they all sell.
Good luck...and most of all, have fun!!!!!
Patti