Highly depends on the type of the trip and expectations.
Up until very recently I was a heavy SLR user equipped with EOS pro gear, so for general trips (be it family vacations of business) my heavy backpack loaded with Canon (single EOS3 body + booster, two large L zooms, flash, accessories) + heavy tripod in luggage. This is provided mixed in-cities waking/inter-cities rented car traveling. Made my back sore, but managed.
For dedicated nature trips - only my LF (4x5) goes with me - still take a lareg backpack but surprisingly not heavier that my previous Canon.
Now converting to RF (Leica M6 with current 50mm/2 'cron coming...) so here is how I can lay it down:
1. Business trips - Leica only (single body) with 1-3 lenses (for teh timebeing will only have single one - 50mm, so will me Leica with single lens).
2. Family trips (abroad vacations) - most certainly Leica only (single body with 1-3 lenses). If there is a large part of the trip that is nature - deicated (out of cities and any lareg population) and provided rent a car - my large backpack with 4x5 goes (+ 10 holders, a pack of 50-100 sheets, changing tent, meter, etc), Leica will also be the companion serving as main tool in general shooting.
3. Dedicated photo trips (so far did only few short ones) - used to go with LF only, now will probably take Leica as a backup.
As was mentioned - all depends on planning and expectations.