I would answer that differently today than I would have yesterday, and might have yet another answer tomorrow. It depends. Spontaneity would probably always be in the top three, though, because it includes so many other "used to's".

Very closely aligned with that would be reliability. For the same reasons I can't do things spontaneously, I can't make commitments. I hate hearing myself saying, "I will if I can" and knowing I probably won't.

The first thing that came to my mind when I saw your question was...walking. I don't mean just getting around--I use a cane when I'm out and about, and I'm a wall-walker at home. And I'm thankful that I CAN still get around! But I miss walking around the lake, around the "triangle", to the school and back. I was always a walker.

Sometimes I'll randomly see someone just walking along the road or on a sidewalk--not jogging, not running, just walking briskly along with no cane, and I feel the tears well up. I mentally say to that person, "Don't take it for granted."

Today, that's what I miss the most.