I find a height-adjustable chair an essential accessory when observing. The longer you look through the eyepiece the more you see. This is especially the case for clusters and galaxies. I would also find sketching impossible without a chair.
The homemade Denver chair folds flat and doesn’t take up a lot of room when not in use. It is comfortable and sturdy but as a consequence quite heavy with the base being 9Kg and the seat 3Kg.