As I recall... from what I have read on one of these forums somewhere, your tire will be very noticeably down tomorrow. I have found the CO2 so easy to fumble around with and spew the stuff out that I just bailed on it after a couple of tries. With a pump you can practice at home inflating your tires so that when the time comes in the real world, the process is familiar. There's something to be said for that.

Here's a link: http://www.rei.com/product/716810

I have the cheaper model without the guage. Again, I strongly advise practice so that you are familiar with how these things work. And they do work.