If I am flying, I try to keep it to four. M8 and M7, maybe the G2 Contaxes, plus something to pocket and shoot snaps. Four sounds like five when you count the small digitals.
If I am driving, I will carry M8, M7, some MF, Fuji GSW, and maybe the Blads.
Possibly the Fuji folder for the pocket.
I have yet to return from Prague without a half dozen- dozen, more, some minature to add to the living room decoration. If I find a nice old Leica, I try to shoot some with it. The "Luggage Facists" and low dollar may have lightened my overseas return luggage.
It's harder to pick and pack cameras than clothes.