Over the years I have used just about everything including rocks. Spruce tree branches work well too if you use them right, the needles will wipe and hold allot crap. Just make very sure that you wipe with the grain of the needles and not against them.
Some members here mentioned snow. I did that once with total regret. I made a nice snowball and used it only to have a major melt down with allot of heavilly contaminated brown water everywhere, on my hands, running down my leg and all over my clothes.
oh LOL, brown snow cown anyone?