Two would be really hard, but if I had to I could get by with three. To start, I would go with Green Dot and a Garand suitable powder (4895, 4064, etc.) Green Dot will do all my light/moderate pistol and all shotshell except .410 bore, plus some cast bullet rifle. The rifle powder can load everything I shoot at full power with jacketed plus be safe in my Garands. However, I would need 2400 to do full magnum pistol, cast rifle, and .410 bore. If you truly demanded I limited it to two I'd probably give up full power rifle shooting and go with the Green Dot and 2400. I enjoy cast rifle more, and I consider myself a shotgunner first and foremost.
These may not be the optimal choices for e erything I listed (or even what I currently prefer) but they can cover it!