Stash at least a five dollar bill into your car/backpack/wallet that you don't touch unless it is an emergency. If you can afford a twenty all the better. The point here is to make sure that you have some cash on you at all times. Don't make it a denomination that is going to tempt you if you happen into Saks when all their leather purses are 50% off - making that 500 dollar bill the exact change necessary for the purchase *wink*. On the other hand, managing to stow away one George Washington is going to get you all the way to nowhere if you need cab fare in the middle of the night. Lastly, really don't touch it unless it is an emergency. In other words, getting a hankering for chocolate ice cream when you are not conveniently located next to an ATM machine is NOT an emergency, no matter what you try to tell yourself as a rationalization.