I'd bring a camera I was already very familiar with, that I'd been shooting and testing a lot, and was comfortable carrying.
- If that's the A7r for you, bring two chargers and lots of batteries.
- For me, a small kit of three lenses (and I use almost exclusively primes with the A7) works best. Which ones depends on what I'm after and what size bag I'm willing to carry, but the Think Tank Photo "Mirrorless Move 30i" man purse seems to have enough room for two A7 bodies plus up to three Leica R lenses, plus room for a bunch of storage cards, batteries, and tripod mounting (if I felt I was going to carry my tripod).
- At most, I'd stuff a Nikon SB-30 flash unit + RF trigger in a side pocket for that very occasional moment when a little bounce or fill light is important. I almost never use flash other than for table top product shooting.
Now which three lenses is always a matter of some debate and last minute decision making. The 35-50-135 or 24-50-90 setups work well. A widely spaced 24-50-135 works well too. Longer than 135mm requires a bigger bag, sometimes including an ultra wide in the 20mm or lower range is just the thing too. But I almost always want a normal (35 to 50mm) along with something a bit wider and a bit longer... it's really just a question of how much wider or longer I'm in the mood for. I've gone whole trips with just a 50 or 35 mm lens being used.
Basic rule for me: the less I carry, the more photography I do.