Large bags of spinach needs more ventilation to keep moisture low. poke holes on the front and back to prevent moisture build up and rotting.
You can also get fresh produce storage containers ( https://amzn.to/2upeJKN ) which have vents for the fresh produce to breathe and stay dry.
Or you can get it in a can of spinach:
spinach, costco, how to keep food from spoiling, food storage containers, fresh produce rot, how to keep spinach longer, how to keep spinach fresh, how to keep spinach from rotting. food rot. how to, buying bulk produce, buying from farmers market, storing produce