I have squeezed (just for an experiment) 6 days' food for both my dog and me in the Weekender. That took a lot of squashing, including breaking up my dog's kibble! I left out the first day's food, since it doesn't have to be in the canister (unless you're going to go away from camp, leaving the food alone, before you eat the first night's dinner).
You want really compact food, such as couscous, rice, quinoa, etc. (Substitute couscous for other pasta.) No crackers or other fragile items. No bulky packaging, and remove as much air as you can from plastic bags. Don't vacuum seal, though, because that leaves the food a hard unmalleable brick. You need malleable items that can be squished into every possible open space. You then push down really hard as you pack each layer of food inside. Be sure to pack the second days' food on top so you don't have to unpack the entire canister for the second day's food--you'll probably not be able to get everything squashed back in! After that, repacking won't be an issue.
I've been able to get 3 days' food for 4 people (2 of them of elementary school age, though) into the large Bear Vault (about the same size as the Bearikade Weekender), which amazed the Olympic NP ranger who gave us our permits. What I didn't mention was that this didn't include the s'more ingredients, which I stored in a heavy plastic jar the first night. Of course on the Olympic NP coast the danger is aggressive raccoons rather than bears. I since bought the Weekender for these beach trips because the kids now eat a lot more, so the marshmallows, etc., are now carried legally! However, with their dad carrying most of the food, my Weekender contained only the light fluffy stuff, which only half-filled it.