if it has to be a vacation photography will for sure be present but not the "first" thing. Therefore I try to keep it simple, last year for a week in Sardinia it was my Bessa R with the Heliar 50 F2 and five rolls of film, by the way I only used 3 1/2. In that occasion I decided for the one camera one lens approach, decided the lens had to be a fifty and decided for the Bessa instead of the M7 because less worth, I could leave it in a bag on tha beach when bathing without too many worries.It worked ok.
Last month I spent two week in Ischia (Island in South Italy, Naples area) and wanted to do something different: I brought two Polaroid cameras, a Land 340 with three pack of Fuji color film and a basic 600 with a few packs of films by Impossible (a few were old and expired), leaving one camera in the hotel and bringing with me the other, depending on the mood of the day!
So what? I have not a fixed solution, it depends a lot on he kind of vacation. Mainly trying to keep it simple!
robert