I recently sent a package out to Toronto and one to Kelowna and they were my first. There's not much to it, this is how I did it after some advice from BigDan.
1. Get yourself a styrofoam shipping box and cardboard box; just like the ones you had fish arrive in at the store you once worked for. You can also line a box with styrofoam you can buy at any hardware store.
2. Punch numerous holes in 2 sides to supply the heat packs the oxygen they require.
3. Tape a heat pack to the bottom or side.
4. Cover heat pack with crumpled newspaper.
5. Place ventilated container in and secure with more crumpled newspaper. For added comfort I placed the snake I sent into a snake bag and then into a paper towel lined rubbermaid which was well ventilated. Cover with more crumpled newspaper
6. Tape another heat pack to the lid and your pretty much done.
Just make sure the container is suspended securely away from direct contact to the heat packs or the sides of the stryofoam.
The receiver of the snake I sent was very happy with this packing job and the snake arrived toasty warm.
Just another note, unless you are a "known shipper", the shipper will require a quick inspection so don't seal up the box till after it's done.
I hope this helped.