If you're just taking a debit card and a few bills a rubber band should work great! Personal preference always tho.
Dr B's shows up at just about any hiking specific store. Or order it from Dr b's website...
I don't know the densities of DEET and water but the weight is probably the same for all intents and purposes. The reason I originally started mixing it was to make it easier to apply to the body. Like I said earlier, you could just do all DEET if that works for you. The reason it saves weight is because you're only carrying a fluid ounce of it in a dropper bottle. Much lighter than any other bug dope applicator/fluid I've found. And it lasts forever because of its high concentration I find that an ounce of it will last an entire hiking season or more.
FBC will save you weight because you can carry an alcohol stove in most situations and a small pot for boiling 2 cups of water. You can minimize your cook set to the point of sub 4oz for stove, screen, and pot. Less than the reported weight of a single empty canister fuel from your list.
If you're on an all out war against ounces these suggestions will help. If you have your own method and system then I'm sure you'll do what works best for you.
Good luck!