The Emergency Twenty

Do you carry emergency cash in your wallet, bag, or maybe car?  My family is debit card based, and I often find that I would like to have a bit of cash on me for something or another.  I always try to carry an emergency $20. (Tucked away separate from the few bills I know I'll spend right away.)  I'd like to upgrade it to $50 or $100, but for now it's a $20.  (Note: If I DO upgrade, I'll likely keep the bills small anyway.)  Here are a few things it could be for.

• Cash "thank you" for someone who stops to help change a flat tire or jump my dead battery
• To cover the items that "grandma" in front of me can't afford at the grocery store
• Unexpected trip through McDonald's to quiet the kids for 15 minutes
• A meal and cup of coffee for someone on the street less fortunate than I
• To pay for the next couple of customers at the Starbucks drive up
• To drop in the donation box I notice while I'm out and about
• To indulge at the only ice cream shop left in the world that doesn't take plastic yet
• A girl scout cookie seller ambush

What else do you find you need instant cash for in your life?