-An unscoped .44 magnum, definitely
-Axes in the vanilla game (come on, there are raiders everywhere with such esoteric weapons as Chinese officers' swords, why no axes?)
-A few more different types of assault rifles/SMGs
-LMGs
-Proper shotguns, that are slightly more accurate than in FO3
Also, I'd like to see different weapon attachments, such as scopes/silencers, and more accurate/powerful/slower degrading weapons in general. Ammo should be sparser, though.
I totally agree with all, with a few additions:
-Besides axes, why not crowbars? Wrenches? Hammers? FO2 had a wrench. And they're laying around everywhere.
-100,000% agreement with proper shotguns. Not another Russian submachinegun, please! And yes, the spread does need to be a bit tighter...
And about repairs, Attachments may not be a bad idea, but we shouldn't go overboard.
I like the idea of a gun cleaning kit. Instead of repairing slight wear and tear with a whole other weapon for spare parts, we have a kit that is good for twenty or so small repairs. Once it's used up, we go and buy a new one (and they'd be semi-rare).