Full Camping: If you want to camp and hike like you would at home with with complete camping gear its best to bring your own gear from home. Failing that Kathmandu is the best place to buy camping equipment. In India try major cities like Delhi and Calcutta, but invariably you will get better priced better quality gear in your home country. You can by substandard overpriced gear in Leh and Manali. The benefit of having your own full supply of camping gear is you can pretty much go where you like, or at least where the authorities let you. Of course the draw back is carrying all your own gear and especially food is heavy and when you are crossing over 5000 m plus passes its really heavy. Food is generally the limiting factor, carrying all of your own food for much more than a week trek in the Himalayas is tough to say the least. If you are going on a longer trek where you need to be completely self sufficient it may be necessary to hire porters or pack animals.
Clothing (type depends on season and region), comfortable walking shoes or hiking boots, food, map/guidebook, water bottle, water purification method, tent, stove (multi-fuel stove recommended for many areas do not bring one that only takes exotic clean burning fuels which are only available in the west, good sleeping bag, sleeping mat, trekking pole or walking stick, compass (if you don't have a good sense of direction), medical kit (tweezers, small scissors, bandages, antibiotics for diarrhea i.e. cyprofloxin, basic pain killer, cold/cough medicine, ect.)