Usually none. I use my card to make purchases whenever I can. I get Amazon points for using the credit card, so I prefer that method of payment. If I know I'm going to need cash for something, I just withdraw enough for that specific transaction. I usually throw $100 or so in my wallet if I'm going to be traveling just so I have cash if needed.
In my old town, there was a big farmer's market right across the street from my workplace. A bunch of the stands only took cash. Since I liked to grab lunch and groceries at the market, I'd usually take out $60 and spend that over the course of a week or so. I had to make constant trips to Coinstar because I would accumulate a ridiculous amount of change from all those cash transactions.