I mostly hunt with single shot rifles now last 8 deer have been shot with them = I understand the one bullet concept but I always take extra bullets with me.
Re detachable mags I like to take 2 - 3 depends on there capacity I still carry more bullets than what are in the mags though example my Ruger American in 450 Bushmaster I have two 3 round mags for it but I still have 6 rounds in a butt stock ammo holder 3 that are the same as what are in my mags and three heavy 355gr hard cast thumper loads.
If for some reason I lose the mag like the OP did I am still good to go as a single shot.