Cool your casserole before storing it. If your casserole has been sitting out longer than 2 hours, throw it out to prevent foodborne illness.
Covering your casserole with aluminum foil is best if you plan to reheat it in the oven. You can leave the foil on top and help keep some moisture locked in. Or cover with plastic wrap (remove when reheating). Or you can transfer your green bean casserole to airtight containers.
Refrigerate for up to 4 days. However, it’s probably best to use it the following day and discard any leftovers afterward.
Notes
Always check for spoilage. If it smells bad, looks bad, or has mold growing, you must throw it out.
Reheat until the internal temp reaches at least 165°F and serve when ready.