Both Lukla and Namche are full of trekking stores selling things like hiking poles, gloves, windproof jackets, cold-weather sleeping bags, head torches and day packs, as well as books, energy bars, snacks and the usual tourist tat. You are much better off buying everything you need in Kathmandu, where prices are lower, or before you go. Outside Lukla and Namche, options are much more limited: don’t plan on finding anything more than loo roll, snacks, drinks, batteries and possibly the odd pair of woolen gloves in many villages.