As for taking one out in the wild, you can take your regular machine or get another one on Craigslist that you won't mind it getting dropped from a tree. The Resmed S9 series are two parts. One is the humidifier and is removable. It is very lightweight. If you want a better one with some kind of warrenty, check out Supplier #2 in the supplier's list. They have gently used and open box machines, some are available without the humidifier which drops the price. You don't want the humidifier since it is a huge power draw when on battery.
There's also a CPAP that is ultra lightweight and about the size of a soda can. Crap, can't remember the name. Inspire?
Read through this thread and check out what others are saying and suggesting. There's a battery pack that is rechargable that some people use.
Apnea Board Moderator
Breathe deeply and count to zen.