What should I add to my fitness routine on the elliptical trainer?

I do 35-50 min. a day on the elliptical trainer and feel pretty good, firm, etc. Workout feels pretty complete as is but I wonder if I'm missing something. Slipped disc means just about all stretching is out so no yoga, pilates beyond a few acu-yoga moves for pain relief. I also walk a lot, swim and may take up skating again this year. Snapping shoulders are a bit of a concern. Any ideas?