It would help if we knew roughly where you are, and where he is, and expected shipping times. Also, how do you plan to ship? Via Delta, or Air Express? What are the expected temperatures at the takeoff/destination point, and will the animal be guaranteed to be in a climate-controlled environment the whole time?
Every snake I have ever received has come in a styrofoam box packaged inside a cardboard box. The snake is, size depending, placed in either a small or large deli cup, or a pillowcase, and the empty space is packed snugly with newspaper, which helps hold heat and holds the deli cup or pillowcase in place.
Heat packs depend entirely on anticipated temperature drops. If it is likely that the animal will experience radically different temperatures from its day-to-day norm, it is best to include a heat pack of some kind, but I really don't know what brand to use.
Shipping and the resultant stress dehydrates snakes, but I have never been shipped an animal that had been shipped with a sponge. Usually it's the receiver's duty to offer the animal a big drink right out of the bag, and a quiet place to hide for a few days. For neonates or young animals which lose water faster, some sphagnum moss in the cup will suffice. If you choose to use a pillowcase to hold the snake, don't include anything wet in the packing at all as it will soak the pillowcase, and the newspaper. Also, wet pillowcases can theoretically smother a snake.
I hope this helps at least a little.
--Naamah