There are so many things. Running, God when was the last time? Walking - a combination of arthritic knees and painful feet makes it so hard to walk for long. Getting down on the floor - with the kids, or to look for something I've dropped. OK, I can still get down, but what I miss is being able easily to get up again.
But the thing I really, really miss, above all else, is having a long soak in the bath. Simply because once I'm in, I really can't get out again. I have to roll over onto all fours somehow and lever myself up from that position The last time I had a bath was about 3 years ago when I thought, dammit I'm going to do it! And when it came to getting out I found there simply wasn't enough room to roll over. I managed somehow but it was difficult and very painful!