Busou Shinki. I wish they had that.
Also, snacks/drinks that aren't horridly over-priced. They sell ramune for close to $4 a bottle at fanime. At an asian market near my house, they sell it for about 69 cents a bottle.
Food is typically a little more pricey at cons because of location (like food at baseball games, beer at concerts, etc), it sucks, but it's the law of "supply and demand".
With stuff like ramune and whatnot, it's going to be cheaper at Asian markets because they get it in bigger bulks (not to mention in business with delivery locations, they sometimes get discounts on the shipment costs depending on how much they order).
Dealers usually bring all their stuff by their own means, so they're essentially paying for the "shipment" (gas money, etc) and they pay to rent out the tables there as well, so they usually add to the price to make up for these costs.
But they could have some cheaper alternatives (like doritos and whatnot) to sell to those of us who are just plain hungry and not Pocky partisan.