From Real Life (not mine, thank Bog):

In the woods you use what comes to hand unless you are boyscout enough to actually carry TP. Usually this means leaves or moss. These work well enough, but if you carelessly grab the ones with triple leaves and red stems, where each leaf has a single serration on the outer edge and the middle leaf is serrated on both, you will within the hour begin to hate your life. Your life will descend rapidly past the drudgery of menial jobs, blow right by in-laws from Hell, and leave running out of gas in the Mojave Desert a nostalgic memory.

Allergic contact dermatitis, people; I'm talking about blister agents on your pink bits. Poison ivy (Toxicodendron radicans) is a plant with a message in it, and the message is BEWARE.