No matter what you do, some insurance (especially Medicare and Medicaid) simply won't pay for some medical equipment that you'd think would be standard. One example is a shower seat. If you can't get one through your insurance and can't afford one yourself, you may be able to make do with a cheap lawn chair.
Having an extra wheel or tire on hand is always a good idea if you're in a wheelchair, especially if you're traveling. If you don't have one and need one, pop into a bicycle shop; they may be able to repair or acquire one for you, or help you find someone who can.