1. 5 Gal paint drum (new ones fairly cheap at Home Depot), remove the handle, put it on your treadmill with a board clamped behind it, and away it goes! Swap the board for your wife's pastry roller, for improved operation. Better still if you can get your 30 minutes of exercise in at the same time...
2. For that matter, attach sling swivels to the top and bottom, and you can leash it to your waist as you go for a relaxing sunset stroll with the missus, the tumbler rolling behind you, sounds of the ocean. Romantic, no?

Maybe tie it to the dog, and play fetch? Or to your kids - they always have so much energy, running around the yard.
3. Pour brass and media into a lawn roller drum, and work-out that rough spot on your lawn!
I bought a quantity of cleaned brass off a Sponsor who was using a portable cement mixer - I thought that was quite efficient. Certainly did a good job.
I forgot to mention Duct Tape, but I'm sure someone will.