Nothing like hiking all day to the most epic alpine lake, completely out of breath, only to pass out while blowing up your air mattress. Yes, I'm exaggerating but don't knock it until you try it (filling up your air mattress with a pump sack, not passing out). The Therm-a-Rest NeoAir Pump Sack is designed specifically for their NeoAir line of mattress pads (like the NeoAirXLite), although it will work with other pads that have similar valves.
The primary purpose of the NeoAir Pump Sack is to quickly and easily fill your mattress with clean, dry air (instead of moist, germy air from your lungs).However, apart from saving you from passing out, it also doubles as a dry sack and triples as a relatively comfortable seat around camp.