Nothing is ever completely critter proof. Bear proof, just about, raccoon proof, maybe, but never rat proof. Keeping food in factory containers will help to block oders some, but....

I've used a packframe with a cargo shelf and a bunch of bungie cords a few times to carry 5 gallon buckets of stuff. The only one readily available is the old ALICE frame, but with better straps and pads and a little work it gets a lot more comfortable. In fact, you might even be able to stuff one of these INTO an ALICE pack, which would let you carry the small stuff.

The other option I can think of, if you can manage it, is to use a staff across the shoulders with two buckets, but they have to be balanced.

Or switch to a decent backpack. Knowing more about what you are carrying would help with to make a good suggestion there.