Gifts and gift giving are important in all cultures, but are particularly important in Tibet. It is always appreciated when you show your appreciation of hospitality and assistance by giving small gifts. Keep in mind that in Tibetan culture it is considered polite to decline gifts or renumeration outside of standard commercial exchanges, but that it is also assumed that the giver will be persistent. Visitors often misunderstand this and readily give up after an initial attempt to give something is turned away. Be persistent! Politely force the gift upon the person, and say repeatedly how minor the gift is, how much you appreciated their help, and how it helps you establish a relationship with them (thereby emphasizing the benefit to you). You can always leave it in a corner of the room and walk away, rather than insisting it be put in the person's hands. Also be aware that Tibetans do not make a big deal of gifts and gift opening the way that Americans at least do - do not expect them to open a gift, remark upon it, and so forth right in the moment they have been given the gift. Just make the gift and let it go - this is polite by traditional Tibetan standards.
The most famous gift in Tibetan culture is the "kata", or silk white offering scarves, which are presented to people in a variety of occasions - going away, weddings, upon meeting religious figures, and so forth. They come in a great range of quality ranging from flimsy things not much different than gauze, to very lengthy and lovely silk with embossed designs of various sacred symbols.
Of course Tibetans also greatly appreciate foreign gifts that are hard to come by in their own markets. In the rural areas, a wide range of things are unusual and thus highly appreciated, while in the few large urban areas like Lhasa, many such products can be easily purchased from local stores.
Suggestions for gifts to rural Tibetans:
Suggestions for gifts to urban Tibetans: