I just learned an important lesson. I usually don't bring anything to eat, and just a water bottle. I had a light lunch and headed out around 6:00 - and bonked about 6 miles and two big hills from home. No money, no power bars, nothing. So, an emergency Snickers Marathon or the oft-suggested Payday is going to have a permanent home in my bag.
Also, a quarter. Some kids in the neighborhood were selling lemonade, and I didn't have a single cent.