RE: 30-06 the everything cartridge...
In North America, it would either be that 30-06 or a 300 WindBag/WSM. If I was going after the bigger bears though, I'd opt for a little more power and pick the 300's. But the '06 will get it done for sure without being overkill on any of the lighter stuff.
For a worldwide do it all gun, the 375 H&H is THE everything cartridge.