The best way to not lose track of your items is to store them in your house's storage or create a space in your town or on your island that you won't forget about. If you are out and about, storing things around your town or island can be easy, but I would caution against just dumping anything at any place. If you have a distinct location where you can put your items while filling up your pocket space, you'll be less likely to forget about them and move on.