I always try to have at least $50 cash on me since tow trucks will only accept cash. Something I found out the hard way when I had a breakdown, and only had $20 in my wallet. When I use cash, I can see how fast I am spending it; not so with my credit cards (that is how I spent $1000 more than I intended to during a trip a few years ago, I used my credit card for everything except lunches and bought lots of stuff that added up very quickly).