I get kitty litter in paper bags, (which are not slippery, at least) and a lot cheaper at 20 kilos than at 10, so there's some gain from strength training already.

Also, I had a class on handling fire extinguishers at work, and I could swing those things around as if they weighed no more than *snerk* 3 lbs, and actually concentrate on the fire instead of on the lifting.