Pronghorn, 250 to 500 yards or so, 10 mph breeze, cold and dry: Yep, you guessed it, 7mm Rem for me!
Alaskan Coastal Brown Bear, wet and chilly, dusk, in cover, 40 yards: This is mostly for you guys. Again, I could try a 3" Mag slug in a 12 gauge or a 175 gr Partition in my 7 Mag, but I really ain't equipped to handle big bears.
Texas Javelina(sp?), oppressively hot, no wind, in cover, 50 to 120 yards: I could use the guns mentioned above, but more than likely, I pull a favor and borrow my grandpa's Marlin .30/30 Win with some 170 gr Interlocks or Partitions (sorry if that's cheating).