I don't think that I would ever fill my bear canister directly with bulk food like rice. I have been known to put about five days worth of instant rice into an underfilled zip lock bag and throw that into the bear canister. I was planning for a nine-day trip one time, so that meant eight days worth of food in a Garcia.
I've moved to lighter bear canisters now, so the Garcia may never see another grain of rice.
One guy figured it out. He bought about ten pounds of Robertson's Shortbread Cookies, ground those up with a rolling pin, and poured all that into a bear canister. Maximum calories with no wasted packaging space. No cooking required.
When I go now, I will carry three or four meals worth of instant rice in one bag, two or three meals of couscous in a second bag, and three or four meals worth of instant quinoa in a third bag. Then there are all kinds of miscellaneous soup bases and veggie flakes to cook those with, plus meat and cheese snacks and dried fruit. A unique mixture goes into each cooked meal. But at least half of the bear canister is occupied by three or more big bags.
Also, I pack the bear canister from the bottom to the top. The stuff on top is likely to be eaten first, and the stuff on the bottom is eaten last. That way, I don't have to keep repacking the thing.