I mainly use my F1 Canons, n and N models, and generally carry four 50's/55's in a small bag.
First is a 50 1.4 SSC, a 3.5 SSC macro, a Pentax M42 1.4 super tak. and a M44-2, plus on occasion a Canon SC 1.8 in case I need it.
A nice Zeiss in M42 would be nice or the Canon L glass, but I'm generally very happy with what I've got in my bag, which carries a Canon 24mm 2.8 SSC, a Canon 2.8 SSC 100mm and a 200mm M42, plus the Canon "P" adapter.
Together with a Canon Auto Bellows and ext. tubes, those 50's give me a lot of satisfaction and I'm rarely no able to use a fifty for the shots I want