Take off the bar+chain and wrap them in newspaper. Drain the gas and bar oil from the saw, then run it dry. Wrap the powerhead in a plastic bag(s) and tape it closed. Also, you want to protect any fragile things that might be sticking out of the power. I would cut little blocks of wood to fit over them and tape it to the saw. This is before the bag goes on. Put the saw and bar in a box and pack with your choice of material. Peanuts, wadded up newspapers, lots of bubblepack, whatever you have on hand. Just make sure it will protect the saw.