The most quintessential Cambodian souvenir must be the checked cotton krama that you will see around the necks, heads or waists of every Cambodian you meet. Cambodians like to boast that the krama has a dozen different uses -- some clever, some cute, some cringe-worthy. The most popular way to wear the krama is as a handsome scarf and a symbol of national and cultural pride, hung loosely around the neck over a pressed dress shirt. However, head out to the villages and you'll see local farmers wearing them wrapped around their forehead to soak up the sweat, while village women will wear them as a head-dress. I've used mine as a belt. They're handy for wiping the perspiration from your brow while scrambling temples in the sticky humidity.
You'll see kramas sold everywhere and in the Old Market they start from as little as US$1, however, these are generally made from a polyester-cotton mix and don't do the trick. I love the authentic, quality cotton kramas sold at boutiques like Wa Gallery, which is where the ones above are from.