Micro-economy cash purchases are one of the best ways to ensure small businesses gain the most profit from each transaction: credit card fees for purchases of coffee, newspapers, snacks and other goodies add up for small vendors. As an added incentive you can add your change to the tip or donation jars at many establishments. A few cents per transaction adds up for someone making minimum wage.
On the other hand I’m a huge fan of the debit card and not having to carry around wads of cash for purchases like groceries and gas. As a matter of course larger vendors generally can include the cost of these fees in the cost of goods and/or negotiate really sweet processing fee deals that minimize the impact on their business.