That $5 thing in the bargain bin is a real deal, isn't it? Maybe not. Researchers have demonstrated that people are much more likely to make small purchases than big ones. That's not frugality: it's human nature. You're almost certain to weigh the pros and cons of a big-ticket purchase than something costing just a few dollars.
If you're in the habit of using a debit card, look at last month's statement. What do you see? If you're like most people, lots of small transactions — and they add up fast. Want to save money? Pay particular attention to purchases of less than $10. Carry larger bills: you'll be less likely to break them. Be slow to use plastic. And smile when you see how well this works the next time you check your balance.