Observing Chair
Sitting comfortably enables you to see better! It also means you're more likely to spend more time outside, at the telescope. Since the eyepiece of most telescopes goes through a range of heights, you need a chair where the seat can be adjusted from high to low [see animation].
This is my version of the ingeniously simple Denver
observer's chair.
The main differences between mine and the
original version are: I added a padded seat (heated!) and I made the
cross-piece at the front (the foot) fold away for storage. Very clear
construction plans are available for the original, so I'll just
detail my modifications here. This is a fun project and can be
built in one weekend for around CDN$30. This is excellent value
when you consider commercial chairs cost around CDN$150.
I bought a cedar 2x4 from Home Depot and they cut the wood to length for free. The plans call for 3/4" plywood for the seat, but I had quite a bit of 3/8" plywood left over from making the top ring of my 8-inch. It was quite time-consuming sticking two thicknesses together and trimming them to the same size, so it's probably worth going out and buying 3/4" plywood.
The seat is padded with flame-retardant cushion stuffing. The padding is covered with black vinyl. I placed strips of nichrome wire (wrapped in heat-shrink tubing, as for my dew heaters) under the vinyl. The black box behind the cushion is the controller for this heater, and a 12V motorcycle battery attaches under the seat with industrial Velcro.
Folding foot
The most original part of my
design is the foldaway foot. 
I've read that some people make the
crosspiece removable using bolts, but my simple design uses all captive
hardware and allows the foot to turn sideways and slide up the
leg. To pack the chair away, the upper eyebolt is loosened until it
slides out of its threaded
insert, while the lower eyebolt (which rides in the long groove)
is simply loosened slightly. Both bolts remain trapped within the foot,
so there's no chance of them being lost. The foot is then rotated
through 90 degrees and slid along the leg.
A hole further up the leg
(visible in the grey stair-tread material, in the first photo, for example)
accepts the top eyebolt and prevents the foot from moving during
transport. For increased stability, I cut a small recess (visible in
photo on right) into the foot
which fits snugly around the leg and prevents the chair from rocking
due to a small amount of play in the eyebolts. This could probably
also be fixed by using thinner wood for the foot.
One tip I have is to connect the aluminium cross brace 3 or 4 inches from the ground. The first time I installed the brace I put it quite low to the ground and found that thick grass would push the bar off the screw and cause the chair to fold up when I was moving it. Also, tighten the screws firmly so that the bar's motion is stiff. Otherwise, dragging the chair across gravel will cause the bar to bounce off the screw.
I normally leave the chair fully assembled, maybe folded in half. It's only really worth folding the foot away if space is tight in the car.