I have been blacksmithing for several years and doing demos for about 6 years. There are a few things I really like to do and several that are expected but not that fun. I mostly demo at living history events, usually Rendezvous. I've done a few craft shows and several Fall Festivals.
Be prepared well ahead of time if it is a big event. You don't want to be on day two with nothing to sell. Have several of each item done well in advance with enough stock with you to make a few items while you're there.
I LOVE to represent history and share factual events that involved blacksmiths. Do a little research and come up with some decent stories one to two minutes each. School kids will eat it up and Parents will usually buy something. Be prepared to repeat the stories and be sure of your facts. Realize ahead of time that just about everybodies Grandpa was a blacksmith. Comes with the territory.
I make nails and S hooks while talking, save the involved projects for when you have a helper. Remember little kids eye line and your anvil height are very similar. This is DANGEROUS if you forge weld in the public. No one behind the ropes, period. You don't want to see who has the best lawyer!
Don't take everything you own with you. Try to pare down what you take to just what you need. Nobody cares if you have 75 hammers, just if you know how to use the one in your hand.
Remember to rest occasionally and drink plenty of Gatoraid and water. A weekend event can go from fun to hard work if you are tired or dehydrated. Try to give yourself some down time throughout the day. People do love to hear the anvil ringing constantly, but if you are a part time smith, you won't be able to scratch your nose on day two, much less have good hammer control.
Be safe, have fun!