I am a believer in ponchos, and generally carry 2 for shelter building. Use them in the winter to block wind and rain, in the summer in two layers with air movement in between to give better shade. The military surplus ones are durable but there are lighter ones out there that pack smaller. Make sure they have grommets or loops for building the shelter. I have a Sea to Summit sil-nylon poncho that works well, and a couple of Equinox ultra light ponchos. Space blankets work well but don't pack as small. I have used these types of shelters in many environments, from the sub arctic to the jungle and deserts. I have always found a way to build the shelter even without trees to tie to.