As someone who as sold at a few shows, I would like to say that bookmarks have been going really well for me. You can get a cheap laminator and sell them for pretty cheap. Because you can get about 4 bookmarks per 1 standard sheet of cardstock (8.5 x 11). I noticed that these are popular with the younger adults (roughly 15-25). I think this is because these people are more interested in reading comic and other novels, and the print has an utility use which is nice. Not many young kids I noticed buy book marks.
Sticker are hit and miss I have noticed. According to my sales records their sales spike every other year. Adding new designs to your lot will help, but I noticed that younger people tend to buy stickers. I am thinking of doing a sticker purge sale to clear out my inventory. Demographic (roughly ages 9-14).
Commission are my biggest seller, and if you can draw something decent in about an hour to and hour and a half, you should be pretty good to go. People will flock to cheaper commission though. I have set my commission to $10 once and....I was really exhausted. I ended up getting about 30 requests, and had to mail a few. So, make sure you set your price in accordance to how you see your worth. And you can always increase your price as your skill does.
I would avoid postcard sized prints. It does well for some people, but I have only sold 1 postcard sized print. Most people I noticed are looking for posters. And setting up poster is a commitment. Remember to think about the storage of your stock as well.
Other random things that will help:
Greet people as the walk by. Seriously it makes a difference. Stand when speaking to people if you can, it show you are more engaged.
If you can, get to know the convention staff. If they like you, it will be easier to get a table next year.
Bring other small stuff, not to sell, but trade with other vendors. Its a good way to may art friends, and you can get something cool in return. I got a deck of dnd magic items, because I gave a print to someone. Also, if you are friendly with the other vendor, they will help watch your table when you are gone for lunch, bathroom etc... they may even offer to go on a food run for you. So, if you set up quickly talk to them. Seriously.
Vertical Signage.
And the free stuff you have is a good attention grabber, but you can also do something interactive. I like to have a "sign Me" card on my table to see who decides to write on it. Its integrative, free, and add to their experience and mine. You don't have to do that (a lot of people don't have something like that) but I think it's neat, and if its consistent, you will be remembered for it.
Other other advice: XD
Your first show may not go so well. And that is ok. Mine didn't even make me any profit. Scary I know. But, people don't know you, but if you come back, they will be more likely to buy from you because they know you. Half of sales is relationships. So don't give up.
