People mention shrink wrap and plastic wrap. What you want is Stretch Wrap. Home Depot sells it with their moving boxes and stuff. Sam's Club occasionally has it for cheaper, but I have not seen it recently. I use it with every pinball transport. before you take the legs off, lay the head down and then wrap the machine multiple times side to side, stretching the wrap as you go after the first go around. This holds the head in place and provides some protection. I agree with putting a blanket or cardboard between the head and side rails. I use hardened cardboard corner strips that come in a lot of packaging of furniture and new pins. I tape them in place to the playfield glass with a bit of masking tape. You just need it where the backbox hits the siderails.
If the game is being transported in the open in a pickup or trailer, I also wrap the machine front to back with the stretch wrap. Most of mine are transported in my wife's minivan which is great for transport. Enclosed and lower to the ground than pickup trucks.