Heavy Juggling
A while ago I started working on juggling heavy stuff. The general idea is to improve arm strength and hand-eye coordination by repeatedly throwing and catching massive spherical space-filling arrangements of atoms. I'm good at juggling enough to be able to throw these objects without a real danger of collisions (which could hurt). I've had collisions, but they were all horizontal ones and as such nothing flew in the direction of my brain. That's good. Anyway, I like to juggle heavier stuff. It's sort of tiring, but it's a cool feeling.
Anyway, my dad and I took some spent tennis balls, cut a long hole in each of them, and filled them most of the way with lead shot. This is a really great idea, in that they weigh about 600 g (a little more than a pound) each and they will not break your foot or dent the floor due to the empty space inside where the shot can move around. I got pretty good at juggling these. The idea is to keep building up. I suggest finding some ExerBalls, which go up to 2 pounds, or some small iron shot puts, which range from 4 pounds up. Everything Track and Field is really excellent for iron shot puts, as they come in plenty of nonstandard sizes and the shipping rates are reasonable.
Anyway, my goal is to get good enough to juggle three actual shot puts for a minute or so. This isn't going to come any time soon, but I can do the 4-pound ones I have for a hundred catches, so I'm sort of getting there. Practice and weight training will do it eventually. It's more good arm excercise than priority.