A must have, IMO, would be a specific gun and with that in mind, here are my absolute must haves:
First- Model 29 6 1/2 inch, blue, three T's (Goncolo Alves)
Second- Model 27 5 inch, blue, three T's, (Goncolo Alves)
Third- Model 629-4 Mountain Gun
Fourth- Model 17 6 inch, blue
Fifth- Colt Mark IV Series 70 Government 5 inch, blue
Sixth- Model 66 4 inch
Seventh- Ruger three screw Flattop 44 Magnum 6 1/2 inch
Eighth- Model 686 8 3/8 inch
As a group, any and all model 29/629
As a note of interest (and dispute), were I forced to have only one handgun (God forbid) it would have to be the 629 Mountain Gun. Why? It is the only one listed that can do it all....defense, concealable if necessary, target, plinking, small or big game capable with the proper ammo, and as reliable as they come.