Food bag

I don't know if the PCT involves mandatory bear canisters, but here in CO (and GNP and YNP) my go-to setup is an Outsak with a cuben drawstring liner. I have done rigorous beta testing for both the Outsak and 1.43 oz./yd cuben bags, and I learned that no rodent can breach either of them (Valerie's evil Grand Canyon ravens notwithstanding). The combination of the 2 is pretty damn secure, if a bit of a redundant overkill. With a roll-top cuben bag, not even bugs can get in. Cuben bags can be made to be waterproof, but they are NOT odor-proof. This setup is not bear proof, but with a proper hang in GNP or YNP it works just fine.

Your grocery bag thing scares me a bit. The only breach I've had in the past 10 years was a big gray squirrel shredding a sil-nylon food bag and snagging most of my goodies. Never again, I've decided.

Shopping bags are a no-go. Don't even think about it. Many areas on the PCT (but not all) have requirements for bear-resistant food storage.

In most areas of the Sierras, a hard-sided IGBC-and-Park-Service approved canister is required. In other areas of the trail, you are required to hang your food out of bears' reach (there is actually a counter-hanging technique that was developed by PCT hikers — known as "The PCT Hang").

Once you start reading the guidebooks for the trail, you'll quickly get an understanding of what will be required. You have a lot of research to do!

Sorry, I should have been more specific. I have a canister for required areas and have used it many times in the past when hiking in those areas. I was asking for places where I won't be carrying my canister.

Again, outside of the Sierras, many areas require you to take precautions against bears getting your food. That is where "The PCT Hang" was developed.

Again, shopping bags will not work, nor would they be permitted under the regulations of the areas you'll be in.

For the desert, Gary's advice will work very well; past the Sierras, you'll be in Black Bear territory, and will need to hang your food.

A Zpacks bag or SilNylon will do. Mice are the most annoying problem and the only places I saw or heard them was in established campsites. Never even saw a bear the whole way.

Supposedly, approval for an Ursack in lieu of a canister is under consideration. Fingers crossed…

I bought a Zpacks food bag prior to my hike in Wimenuche Wilderness last year. Never had an issue and was able to stuff a descent amount of food in it. With the roll top, it is easy for bear bagging it up a tree as well.

Contrary to the comment above, I'm not aware of any place outside the Sierra that requires bear-resistant food storage. On the PCT, I slept with my food every night except when I had a canister in the Sierra.

That said, I would just get a regular silnylon stuff sack. They're pretty near indestructible and last a long time. On my thru-hikes, I used a 13-liter Sea-to-Summit Ultrasil roll-top sack. Probably anything will work.

I used a cuben Z packs bag for my thru, paired with OP sacks which I replaced twice during my hike. The OP sacks are of questionable functionality (as several thread here attest), but they made me "feel" better, considering most thru hikers just sleep with their food. It's not a popular admission, but nevertheless true.

Be aware whatever your choice, mice are a problem … particularly in Washington.