Think vertical!
I have several bookstands to display my books, and I have a variety of plastic risers to add height. I have a bright red tablecloth that contrasts well with my books, making them stand out. The smaller items (like buttons) I just lay down on the table, because they're only impulse items and not the first thing I want people to see. I also have one of my original pages, framed with a black mat, on a stand (I'm trying to sell my art, but not a lot of luck so far). It's 11x17, so it's big enough to attract attention. People will often stop by to look at original art, even if the story isn't appealing to them.
In addition to the list TheCow posted above (minus the puppet
), I also make sure to bring flyers, a clear plastic holder for the flyers, price signs (everything should have a prominent price), and an additional tablecloth. If you're at a multi-day show, it's handy to have an extra cloth throw over your table at the end of the day, rather than going to trouble of putting all your stock away and setting it up again the next morning. (This is a trick I picked up from the guys who set up in the dealers' room.) You can also use it if you have to step away from your table for some reason and don't want to ask your neighbour to keep an eye on your stuff.
Also: a fold-up handcart. With big wheels. Indispensable for carting your boxes around a big convention hall.