What should I do on the trail when I get mud caked in my chain, derailleur or cassette?
Mountain bikes weren't invented last time I had this problem.

Since you're already covered in mud, wipe much of it off with your hands. Be careful to keep fingers out of the parts that bite.

Use a stick where it's dangerous to poke your fingers, and get mud out of the derailleurs.

Depending on the kind of mud, and water availability


dunk the whole bike in a puddle or such.
use your water bottle to hose mud out of the important bits.
urine works too ...