It's been mentioned before, and it gets into personal preferences and a lot of logistics/timing, but it's really handy to be shooting identical loads as your hunting buddy. That's not always possible because no two barrels are the same and we are all after optimal accuracy.
My buddy and I decided to have customs built last Spring and in the process reviewed multiple cartridges and decided that the 7RM would be ideal for us (Elk and Mulies predominantly). Ultimately we couldn't agree on final bullet selection, he's shooting Bergers and I'm shooting Barnes, but we both shot each other's ammo and know that with minimal adjustment we'd be back in the game if we had to borrow from each other.
With that, he carries a box of 20 plus 3 in rifle. I carry 10 plus 3, so 36 between the two of us. That's a lot of redundancy.
If it comes right down to it, although we have a lot invested in each of our personal rifles, neither of us is so prideful that we wouldn't abandon our our own setup if we have issues, and switch rifles to make it happen. He missed a bedded buck at 400 this year and I couldn't spot his hit (we didn't know if it was a hit or a miss, we assumed hit). In the chaos after the first shot I couldn't see where the buck ran (down into the canyon and straight at us). He missed again and then at 300 just before going out of sight he took a shot at the neck (only shot he was presented and assuming that the first shot was a hit).
Before going to investigate we discussed the shots. I told him I couldn't see impact on shot one (miscommunication and excitement leading to me not being set up with tripod when he shot). He felt confident in his form but also said that he never saw the buck react like he was hit. We never saw the buck escape out of the canyon and could hear rocks rolling directly under us about 200 yards down the steep rocky ridge we were on. Earlier that morning I took a buck at 260 and we knew that my rifle was still solid. Our hunting style involves a technical dirtbike ride every morning and then a few miles of hiking so it's always possible that he could have bumped his scope. With confidence waning, we both decided that he would carry my rifle during the investigation.
Fortunately it was unnecessary, his buck was piled up where we heard the rocks rolling with a devastating hole in his neck (unscathed otherwise). Not sure what happened with that first prone and bedded shot.