There is hardly any lighting down inside the Man Singh Palace so I suggest bringing a torch with you. I couldn't see where I was going. Tour guides had torches and luckily a party of school children were being shown round so I used their light to navigate. It wasn't much fun in the dark and I left without seeing much (literally).
There are no restaurants or cafes within the fort. There are a few snack stands by the Sikh temple so if you want something a bit more sunstancial then I recommend that you bring food along with you. As for amenities, there are none (or at least I didn't find any). So, the only places to go are behind bushes!