I have an inexpensive aluminum folding camping stool, which is lightweight and stable, but doesn't sit very well. I place a self-inflating foam seat pad on the stool, and the combination of the two is a fairly comfortable seat. Both are easy to carry, and can be purchased at most outdoor equipment suppliers.
2017 Jason Wolverton spruce/maple, 640, "Luz Blanca"
2016 Kenny Hill New World Estudio 640, C
2015 GV Rubio Estudio 640 SP/PE