I'm not as rich to carry a couple hundred on me a day like some of the posters above me...lol But I usually carry around 30-40 Bucks on me incase I ever need to buy a new shirt or food or something.
^Same, I usually just carry $5-10 bucks in case I forgot my lunch at home, or if I need to buy school supplies if I left my pencil, paper, calculator and erasar at home.