1 thin round disc (Frisbee, aluminum, etc), mounted to an appropriate shaft (we use a VersaHub), 1
VEX pancake cylinder, 2 brake pads, two pieces of 1"x1" angle aluminum (~4" length each) properly spaced/mounted and two mount bolts are all it takes for a brake. This is less than half a pound if pneumatics are already used.
The cylinder uses very little air on a single unbrake/brake, but keep in mind that it happens a
lot.