Rifle cartridges: .22LR, .264WM (1:8" twist), .50-110
Bullets: Sierra Varminter, Woodleigh Weldcore, Northfork monolithic solid
Powders: IMR 7828 SSC, Accurate 2495 (don't really need a 3rd powder with only 2 centerfires)

That covers everything. Maybe not perfectly, but well enough. You'd be a little limited for range on thin skinned dangerous game, and a little over-gunned for certain varmints. But you can't have it all with only 3 guns.