Just something I learned on this forum awhile back. There is no real need to carry boards of various thicknesses for leveling side to side. I you put a single board under just one tire, it will lift the rig half the height of the board. A board under both wheels will lift the height of one board.
Another tip some of us learned the hard way
... before you lower the landing gear, check the front to back level. If the nose is high, you will need to lower the landing gear far enough to allow you to bring them back up after unhitching in order to get the rig level. If you don't initially lower them enough the legs will reach their upper limit before the nose has come down enough to be level.