Afghanistan is a different kind of war than Iraq, especially for the infantry. For one thing, Afghanistan requires infantry to spend more times out in the country. This requires them to carry their gear in a rucksack. To make the rucksack easier to use, troops use many high tech items of civilian camping gear. The stuff the military issues is often years behind the latest gadgets available to civilians. So the troops buy the latest items in order to make their lives in the field a bit easier.
One of the more popular items in Afghanistan is the air purge compression sack. This is an airtight bag, for sleeping bags, or other items, with a one way air valve (or, in the latest models, special material that allows the air out, but not in). With these sacks, items can be, well, compressed, so that you are not carrying a lot of bulky (puffed up with air) on your back.