Keep Mushrooms in a Paper Bag, not a Plastic Bag
A plastic bag will trap moisture and cause them to mildew. Put them in a paper bag in the fridge or in a cool, dry place.
I prefer green onions to regular ones and when spring comes, I tend to over-buy them only to discover that I can’t eat the entire bundle. By placing them inside a plastic bottle after drying them completely and putting them in the freezer, they will last long enough to taste as if they were freshly bought.
For regular onion I have another suggestion and although I know that it will bring a couple of smiles, I can’t help but share it with you. Pantyhose are the unlikely storage place for onions, with each vegetable being individually wrapped up with knots between them to preserve freshness.