Does Michael eat proper meals in the Diary Room
 

I cannot imagine him being on rations too.

I think he must pop into the Diary Room, have his grub (three times a day) then come out again just saying' they were asking what I was feeling like today.'

He probably is allowed to shower too.

Doubt it... Too much time in the DR would be too obvious... He's obviously being prepped for instances like tonight beforehand but there has to be an element of realness to what he is doing... Keeping him on the same diet as everyone else seems like an obvious way to achieve that... That being said I don't think he's meant to be in there long TBH... At the most I think it's likely he'll be in there another 2 to 3 weeks tops if not gone by the end of the week...