Sam, You need both. Have some items to sell right then but have samples of your personallized items on display. For example, I make a stool for children that can be a step stool or a chair. I personalize it by making puzzle pieces out of their name on the seat and a little fret work or clay inlay of something like a train or fairy or butterfly. I have one on display and take orders for it. It sells for $50.00 and takes less than a day to make. When you are at a local craft fair or festival, your customers usually live in the near vacinity. I usually take 1/2 down, the balance due on delivery. Then you know they are serious and will make good on the other half. If you have to ship it, know in advance what a flat rate box that size cost to ship and add it. They are usually excited to get your phone call saying it is ready and will meet you somewhere.
The regular items for sale are usually crosses, puzzles, boxes and a random group of items either around the nearest holiday or the theme of the festival. Be careful about town or school mascot items because you can get stuck with a few.