Many of us have long wondered what was in the aft compartment on the port side--something we never saw on TOS. Indeed we saw very little of the starboard side either (which I'm working on presently). So here is my take on it. This is based on the idea of the vehicle having to support up to seven personnel over at least a few hours to several days or even a few weeks duration (the longer the mission duration the likely fewer personnel on board). It's my conjecture that this area in the aft compartment is what the
Galileo crew were primarily tearing apart and jettisoning overboard to lighten the ship's take-off load. My thought is they ripped out (or more likely dismantled with tools) the bulkheads and what they could tear out from behind the bulkheads. My design has large storoage bunkers behind the starboard side bulkhead so they likely threw out whatever might have been stored there as well (possibly environmental suits and assorted gear). Given that two crewman had already died (Latimer and Gaetano) prior to the attempted lift-off then it's likely the remaining crew could have jettisoned two seats now no longer needed, but they ran out of time.
What looks like a familiar toilet is actually the waste management system. Anything that needs to be disposed of (besides human waste) goes into this receptacle that seals tightly before disposing of the contents. A proccessing and recycling system reduces the materiel to its most basic elements and recycles whatever possible into usable elements. If there is anything that cannot safely be recycled then it is either placed into a temporary storage reseptacle or jettisoned into space via a small transporter.
One could also add a form of retractable curtain for additional privacy on the port side of the compartment.
Although it was never explained on TOS the food and matter processing system had to have been quite similar to what was seen on TNG only it was done with the dispensing receptacle covered with a panel. It is effectively a compact transporter system that takes basic elements and rearranges them into new forms. For something like the shuttlecraft which would have a much less extensive system than the
Enterprise the processing system is primarily for a "limited" selection of food and beverages and possible a limited number of other things. By "limited" I mean most likely in comparison to the extensive resources of the
Enterprise while it would be heaven compared to what astronausts must sustain themselves with today.