The classic mountaineering shelter for cold and windy is a bivouac sack - one that is basically just a bag, not a mini-tent. It will weigh under a pound and will keep off wind and rain. Often used when sitting out the night on an exposed ledge, it doesn't have bug netting or any weighty frills.

For sun protection, find some shade or rig a space blanket.Some distance hikers advocate a light weight umbrella if one is moving. Staying off the ground or finding natural shade is a good idea.