I know what you mean, I'm a pack rat too
But one thing I do do is pick up any treasure (including gems and jewels), and any waepons and ammo I find. Then I sell them all (except the ones I want to keep). I did this in the dark ages and modern age (until I got to 90 manipulation
)and I got tons of money. Maybe if you do that you'll be able to get all the ammo you need without cheating at all
(note, if my inventory got full and there were still stuff I cold sell left on the floor, I would come back for them after I sold everything I already have. But this only happened at the Society of Leopold since I had only 1 guy.)
As for any other stuff you're afraid you'll need... I only keep that way vaccines, poison antidotes, and scrolls. And I never need them. Ever. I know I can sell them, but I don't mind having them in my vault. Besides most of the scrolls I keep for fun I forget to use
If you keep stuff like vaccines and poison antidotes than sell them. If you get diseased it won't kill you, only damage you, and most of the diseases (if not all) don't do that much damage, and you can just heal. You can also use heal to cure the disease (I think it only works for higher levels of heal, but if you're in London than you probably already at max). I don't think I ever got poisoned, but if I do, I'm sure you can use heal to cure that too.
As for scrolls... I think the only ones you really need are Awaken and Walk the Abyss (and you only need that one if you don't have the patch installed).
All of the other scrolls you probably already have their powers from your disciplines, or they are weak powers, or you can handle without them.
Oh yeah, and you don't have to wait till you get out of the temple to buy ammo, you can go back anytime you want...