Bought some new (secondhand) cookie canisters from Tupperware.
That lid really seals tightly! I watched dozens of Youtube videos trying to figure out how to close it, attempted to close it 27474 times, both canisters and lids flew all over the kitchen a couple times, and I was ready to dismiss the lids as faulty and resell the canisters again, until my boyfriend figured it out. You have to push the lid really strongly down into the canister, and it closes really tight. You need some strength to open it too But it seals really well and hopefully that will help my cookies last a long time!