If I have extra onion and I want to use it in a couple of days or whenever, I take and put it in a ziplock bag and I take some old bread or buns I was going to throw away and stick in with the onion. The bread absorbs the onion smell and doesn't stink up your refrigerator and freezer. I keep the old bread in a bread wrapper in the refrigerator in the back so it does not get confused with the good stuff.