In the spirit of the thread, I suggest:

.243 Win
.30-06

This covers varmints, small deer and larger deer and black bears.

If it was a more general two rifle battery, then I would like some overlap for the cartridges. Keeping with the varmint theme, at a stretch, I would suggest

.25-06
.338-06

Other than that, I think this provides good coverage - lightweight mountain rifle /better wind bucking and something to hunt larger game

.270 Win
.338-06