In reply to David Kirsfelds:
You will still have your upper body, so why not think of physical things that you can do with that? Weights, darts, wheelchair basketball, gardening...
Then how about creative mental activities? Learn a language, write a novel, learn to sing, build a matchstick model, sew some custom made climbing kit, cook something amazing...
And don't forget social activities - going to the pub with mates, having a film evening, inviting people around for dinner, writing letters to people, phoning people for a chat, visiting people for the weekend...
and then there are all those jobs that you have been putting off forever, the decorating, fixing stuff, tidying out cupboards, things that will leave you feeling that you have achieved something useful.