My experience is that whatever you want to buy costs as much as the seller sees you have.

I keep lots of $1 bills. Not much total $$, but much easier to negotiate if all you have are $1's I keep larger bills in another place and have them so that I can see and get to them in my pack without anyone else being able to see them. I agree that the $100 is the best "realllly need help" bargining tool. I only pull than one when I need to, but it works.

Ok, I keep some of the "ones" in a folded stack in my pocket and have gotten good at peeling off one at a time without pulling the stack out.