A few "stories" about our Alaska cruises.

2010: I rented the 500/4 v1 but had no monopod. I used the tripod on occasions and had a ton of fun. It didn't feel heavy until the trip home.
2012: I rented the 400DO v1 and had no monopod. I also rented a 1Dx and a 1.4x TC, used exclusively on the 400DO. That sucker was FUN! I felt like Quick Draw McGraw: I shoot YOU! I shoot YOU! I aim anywhere I want with a flick of my wrist and I shoot YOU!
2014: I rented the 200-400 and really liked it. It gave me some versatility, and although I learned to think of it as a 200-560, I eventually got tired of the only 2x zoom range and the not-all-that-impressive aperture (given the physical size/weight). On the premise that most of us shoot zooms at either ends of the zoom range and rarely in the middle, it made carrying a 70-200 almost redundant. Not totally, but almost.
2015: I rented the 600 and a 1.4x and fell in love. Paired with a 100-400 and a 16-35, I rarely felt that the 35-100 hole was a problem. I got really comfortable carrying the 600 on my left shoulder, sometimes even hands-free (I probably put a lot of stress on the EF mounts, but I found that the 1Dx/1.4x/600 combo had enough length to fit on my shoulder, and the collapsed monopod still put the center of gravity down low enough that it would stay put). One time I did try the 600 on a Wimberley head on a monopod: too much weight and too squirmy to carry.
2017: 600/1.4x again, only this time on a 5DsR. Damn. Erectrifying, if you know what I mean. I ended up with a 70-300 on my 1Dx (wife "claimed" the 100-400; I may rent a second 100-400 next time) and a 24-70 or 14/2.8 on a 5D3.
Next time, I think I'd leave the 1.4x home and just crop if necessary; the 5DsR isn't as forgiving if you push the ISO so keeping the lightway open helps. If I do skip the 1.4x, I'll probably stick to the 70-300 and also punt to the 16-35 and leave a lens home or perhaps bring a Zeiss Milvus 100/2 Makro "for something completely different".