Free: Contests & Raffles.
Compression bag for food?I've got a couple REI Compression bags that have worked fine for me. I just put food in a stuff sack.
Granite gear makes a couple of different weight bag types...Backcountrygear.com etc...
I use the OR bags mentioned above. They work great. Looks like they don't make that style anymore. You can order the newer styles directly from OR (Seattle-based company) on their website without setting foot in an REI if that's an issue. http://www.outdoorresearch.com/en/or-gear/storage-systems.html
I don't use em...they're just extra weight. I fit food in to the spaces that are made by the bigger items and then put it all my sleeping bag sack to hang when I get to camp.