Depending of what you have already and if it’s guided or DIY: $ toward a good pack, Quality headlamp, ultralight pillow, bino harness, trekking poles, or amazon kindle for reading books (lighter than a paperback and can hold 100s of book.
Or a good piece of clothing for your kit depending on expected temps - down puffy, gaiters, mid layers, good wool base layer set, or even zip off long underwear. Zip off long underwear are hands down my favorite for when I am doing big climbs and then sitting for a few hours afterwards. Make it much easier to regulate temperatures.