A good bathroom break, and maybe making it through a weekend without beer. Not sure how likely that is though.
The low level cardio, i.e. the steady state, I think you can always get away with. Really all that should be doing is replacing normal activity if we weren't most of us so desk-bound.
Prowler/sled stuff you need to time and program correctly. Either after lower work, and/or the next day. I also think it should be dialed back a little the last few weeks before a meet. I think it helps considerably though, I have training partners who struggle to get through their main lift, much less assistance work, and always drag through a meet.