I'll be joining my 6th convension this April and honestly the first 5 times I've done this what sells the best for me is usually just prints. A5 prints to be specific, people seem to like smaller prints where I'm from but it's different from country to country, stickers do really well as well.
I personally don't sell comics or books in general, it's too risky bc it's expensive to make and you can't garantee they'll sell well and I've seen so many people suffer bc they made artbooks that costs a lot to make.
Here is the advice I can give you from my own experience:
- Take your time to find a good printing press, find somewhere that prints cheap but with good quality or a place with flexible prices so you can get a good offer on printing a lot. The place I go to prints A4 Glossy paper for less than a $1 and I sell the prints for $10 and I turn out a good profit and it's bc of the printing.
- Draw fanart but have a mix of both fanart and originals, some people would notice your fanart first and might like some of the originals as well.
- If you want to make originals, have an interesting theme or a theme that you know people like about your art. Like I know a lot of my followers like it when I draw flowers or space so some of my originals had a floral theme going on or had stars/galaxy themes and when I started doing that my originals sold out faster than the fanart.
- Stickers are great, I usually even have a buy 4 get 1 free thing so everyone picks up 5 and they finish quickly.
I hope that helps? I've personally had a good experience selling at cons and usually make a good profit, if it's your first con it might be difficult but once you get the hang of it you'll know what sells well and what doesn't and you'll know what products to cut out or make more of.