I highly recommend keeping at least one Chawly Changer in your car - especially if you live in a city, where you are constantly having to feed the meter! This little gadget saved my day this past weekend. After finally finding a parking space in DC, I looked in my wallet only to find several pennies. Luckily, I had filled up my Chawly a week ago and had enough money to fill the meter for a couple of hours. A must-buy for you city dwellers!