While many people debate whether Comic-Con is about Hollywood or comics, I know that at its core, Comic-Con is about BAGS! Fans will wait hours in line to get a Watchmen or Pushing Daisies bag, or of course a Viz bag (my favorite, the red one from several years back, is going for $50. on eBay).
There are plain old plastic bags.
A detail of one of the large plastic coated paper bags.