Make sure you don't buy anything for those who did not even bother to give you a phone call during your entire 15years stay in the US. They will now make you feel that they really are the ones who cared for you the most (tini harula lai bhanta dinu nepal mai paincha). So, based on this you will only have handful of people to remember or buy gifts and don't hesitate to spend money on their gifts.
This is what I did when I went to Nepal last December after 10 years of my stay in the US.