foam mat roll, exactly like this, from harbor freight (or wherever).
cut it into squares or narrow strips, or micro(for easier packing).
why: save your butt. softer than sitting on rocks, gravel, or concrete.
benefit: cheap, light, effective.
cons: easy to forget (thus leave/lost risk) , often packs awkwardly.
*tip: large pieces double as shading tool eg when walking in the sun.
Another dual use is to line your food items carrier (in case there is one) with someone’s foam pad, and it’ll insulate the food from the direct heat of the sun.