I was originally going to do that at AC, but Starbucks pretty well prevented that.
I'm not sure what merchandise I'll have. I'll have myself and my ability to draw sketches on demand for starters, of course ... beyond that I hope to have buttons, some prints, possibly a portfolio, and mmmmaaaybe t-shirts. I figure I'll probably start with a Tiffany shirt, a Drezzer shirt, and maybe one of either a Dover shirt or a "Watering Hole" shirt. Really, that all depends on how much cash I can arrange to have to pay for the printing of the shirts up front. I'm hoping, between various contributors and my own investment, to have about $500 to spend on it.
My initial goal is basically to recoup as much as possible of the costs of travel and hotel for the con. If I can get somebody to share the room and/or split the table, that will help. It would be nice if it actually made a little profit, tho ... my first goal is going to be to pay back contributors. My next goal will be to expand the merchandise selection.
In doing all this, the primary motivator isn't to make a living, because that's not going to happen. The primary motivator is to pay for going to cons every two months -- because otherwise the cost is right through the roof! But I looooove going to them, and I don't want a little thing like money get in the way of it!
So MFF is my test bed. It's a smaller, more laid-back con, and has much lower costs involved. If I can get MFF to pay for itself, then hopefully it will be a short step up from there to doing the same at AC, and then (in time) Further Confusion and Dragon*Con, both of which are hefty expenses for me.