I'm finding that needs and uses for a battery changes over time. This is what I consider my basic battery for all practical uses:
Handgun: 40 S&W seems to be the most practical and easiest to scrounge ammunition for from local LEO's.
.22LR Hunting (Ruger 10/22)
5.56/.223 Defense/Hunting (AR is very versitle and can be used for both)
.300WM Hunting/Long Range Defense
12 Guage Hunting/Defense
While I like the .308 you will notice I selected the .300 WM as my choice in this battery. I did so, not because I find the .308 lacking for most applications but because of the greater range at which larger game animals can be taken. I tried to look at this from an all possible scenarios viewpoint, and while the .308 may be easier to scrounge ammunition for, one can always pull the .308 bullets they scrounge if they save their cases.
If I was to add a second centerfire rifle I would scrap the .300 Win Mag in favor of the .308 and add a 9.3 x 62 or .375 to the mix.
First, let me say that I'd likely agree that for a one rifle big game hunter a .300 mag, as you chose, likely makes the most sense. I, for sure, like the 2 rifle idea though, like your chosen .308 (a great round) and then a heavy rifle like 9.3x62 or .375. I have a 9.3 and like it a lot, but I'd also suggest if you ever get serious about looking, that you think about the .35 Whelen as well. It's taken far too long for the Whelen to become entrenched, but it finally seems to have a firm hold with hunters wanting a medium, medium bore. Close in performance to the great .338WM, but not nearly so difficult to handle.