Glock 30
CZ .223 bolt
Remington 1100 LT-20
Ruger 10/22 (aftermarket stock, trigger parts, barrel)
S&W M&P 9c
These are based on weight, ammo availability, accuracy, dependability, and expected targets. Depending on circumstances, an AR-type .223/5.56 or Remington 700V .308 could replace the CZ, a Beretta 3901 12ga or Mossberg 500 12ga with two barrels for the LT-20, a Savage 17HMR for the 10/22, and a G35 for the M&P - but if I HAD to pick 5 to keep or take with me into a survival situation, those would be them.
The only one without an alternate is the G30 - that's one versatile bad boy! None of my 1911s, S&W wheelguns, or .22-250 Varminters makes the cut, even though I enjoy them (and the CZ) the most of any I own.