One of our old tricks for getting unstuck if we had no winch or tow vehicle was to rig a logging chain or cable to a tree a good distance away and pull it up as tight as you could by hand.
Then go to the center of the cable and pull it sideways.
You can get a really impressive mechanical advantage that way.
You might pull the cable 8 feet sideways and move the vehicle less than a foot, but you can pull it really hard for that foot it travels.

Be careful though, bumpers can come off and frames can be twisted.