Well, there are times at a con or a longer troop where carrying a wallet/phone/glasses or even a hotel key are ideal. The neck wallet is something I like because I don't have to take my armor off to get my money and buy a coffee. The magic drop box is a nice idea if all you need is a credit card and hotel key.
So if it's a canon event I go with the neck wallet, otherwise I like having a side pouch (I have a plastic one that Terry Chui made, and a leather one Darman made). This way I can put all my stuff in there (like my reading glasses) and can be gone for hours at a time, self-sufficient. I guess once I'm suited up I don't like having to take anything off to get to my things.