I keep a bag of setting compound anywhere from a few weeks to a yr or more. I've never done anything other than fold over the opening in the bag and store it in a dry place. Never had any issues. I'd be a little concerned that storing in a plastic bucket would have issues with condensation.
Suggest putting them (bag or box or can or bin) in two layers (double bagged) plastic leaf bags, trash bags, kitchen bags, or even plastic grocery bags depending on size. Two or more in one bag is okay. Add dessicant pack if desired and available. Squeeze out as much air space as you can, then use twist tie to close the bags.
A forum community dedicated to Do it yourself-ers and home improvement enthusiasts. Come join the discussion about tools, projects, builds, styles, scales, reviews, accessories, classifieds, and more! Helping You to Do It Yourself!