The single most useful thing you can contribute is your self, your time and energy. There's a powerful, universal need to know and be known, and in the process of meeting it you'll get a direct sense of what material needs you can best help meet yourself. I helped with paperwork/minor repairs to get three different crews set up in abandoned beaters I saw walking around last year. You don't have to be homeless to walk into the warming shelter and just start participating. Cannot recommend it enough, especially if you're feeling isolated or getting too much screen time. You are wanted, you are needed, and you can be someone's hero.