mad money
1. A small sum of cash money kept aside or in reserve for emergencies, unforeseen expenses, or impulsive purchases. Whenever we travel, my wife and I keep a small purse of mad money with us just in case we find ourselves in a difficult situation. She likes to set aside a little mad money when she's doing errands each day, so she can buy something nice for herself if she fancies it.
2. A small sum of cash carried by a woman to pay for the fare home in the event of her quarreling with and separating from her date or escort. My mother taught me to always have a bit of mad money on me when I go on dates, just in case things turn sour at the end of the evening.