Many items only appear in the DLC's like the:
FNV
HH: .45 Auto pistol; .45 Auto submachine gun
LR: Breathing mask; Bowie knife; Flare gun; H&H Tools nail gun; Industrial hand; Satchel charge;
FO3
OA: Trench knife;
TP: Radier Armors; Filtration helmet; Infiltrator;
PL: Double-barrel shotgun;
I think all of this list a fit to used more throught the games.
What do you think ?