Bruce, you can always play along with records, or (even better) with other musicians. Some folks may not consider this "practice," but if it's a choice between doing that and giving up the instrument, I'd give it a shot.

Frankly, I've always wondered that about a lot of instruments. Keyboards and guitar can sound pretty complete by themselves, because they're polyphonic, and because they cover a fairly wide tonal spectrum. Most other instruments do not have these qualities -- as a guitar player, it's a wonder to me that anyone sticks with them.