Forgot to mention it, but snapper used to make a huge, plastic "box" that went between the handle bars and took place of the bag. I think it was called the "Pac n sac". It held a lot more grass than the cloth bags. I don't know if they make them for the newer models, but you can find the older ones on Ebay every once in a while.
There's also the snapperizer attachment that really shreds the gras and leaves up, allowing you to get more in the bag, but its pretty expensive