Whenever you need to transport your snake, place him in a cloth bag, such as a pillowcase, and place the bag inside a rigid plastic container. The opaque bag prevents the snake from escaping the box and tends to reduce the snake's stress level, as it prevents him from seeing all of the activity going on around him. The box helps to moderate the snake's internal temperatures and protect your animal from injuries. If this sounds like too much work, you can opt for a commercially produced snake transportation container.
Virtually any type of soft, durable fabric bag will work for temporarily containing a pet snake. In practice, most snake keepers use old pillowcases or commercially produced snake bags. A standard pillowcase will contain snakes of about 5 feet comfortably; use larger bags, such as those used for laundry bags, if your snake is longer than 5 feet.
Your snake, like other reptiles, does not require as much oxygen as mammals or birds do. The snake can breathe comfortably while inside the bag. If you are in doubt, see if you can breathe through the fabric -- if you can draw enough oxygen through the fabric, your snake can, too. Place a few pieces of balled up newspaper inside the bag to help absorb any fluids your snake may release. Place the snake in the bottom of the bag and tie an overhand knot in the top of the bag.
Select a box large enough that your snake can lie comfortably in a flat coil on the bottom. Ideally, the snake should be able to feel the sides of the box with his body while lying comfortably, which will make him feel more secure. Plastic storage boxes work well, but a 5-gallon paint bucket or a small cooler will work for some snakes. A cooler will provide the additional benefit of keeping the temperature inside relatively constant.
If your snake will be in the container for only a brief time -- no more than two hours -- the plastic container does not require ventilation holes. In fact, ventilation holes reduce the thermal stability of the box. However, if your snake is going to be in the box for a long time, it is wise to drill a few small holes to allow air exchange.
Do not bump, jostle or invert the box while you are transporting it. Instead, carry it gently. Keep it nearby for the duration of the journey. Keep the plastic box out of direct sunlight, and use the air conditioner or heater in your car to keep the box between about 65 and 75 degrees Fahrenheit. Use a digital thermometer with an extension probe inside the box to monitor the internal temperature.