There was an article some time ago about this
http://www.boston.com/news/local/ar...reative_savings_5_can_get_you_at_least_12000/ and someone posted here in the Budget Board. I tried it and it works. BUT
You have to be someone who spends cash anyway. In my budget, I get a certain amount of cash each week. With that I pay for things like eating out, coffee, running in for a gallon of milk, giving my kids money for _______, etc., pedicures, etc. It's basically my misc/mad money, not for my usual budgeted items like groceries or the like.
You have to be disciplined. Don't spend those $5 bills! I put mine in a separate section of my wallet so I didn't even see them. When I got home, I put them in an envelope in my secret spot at home.
You can't just go get more cash! Stick to your budget. If you run out because you got a bunch of fives, then you wait til next week. It may be difficult for some to follow this.
The first year I did this, Aug 2008-July 2009, I saved about $1000. The second year I didn't do quite as well, but close--it was about $900. I have "sort of" done this since then. I didn't have a trip or other specific thing to save for, so it made it a little more difficult without the motivation!
It really stinks when you go to the drivethru at Sonic for a drink, pay with a $20, and get 3 fives back in your change!
However, it made me think twice a couple of times, about spending that on drinks.
(oh, and even now, if I have cash left at the end of the week--it doesn't happen often!--I put it in my Disney envelope)