FlyinJake is on it. CashCards. If you are in the United States, you can get CashCards at Walmart, Circle-K's, even at American Express, from what I hear. So, basically, a cash card, like an ATM card, is 'cash' with a plastic number, so you can use it digitally online for purchases of planes, a simulator (wink), iTunes, etc.
If you have a bank account, you could use PayPal. That is 'cash' basically. They do have credit, but you dont have to use it. I dont. I have an ATM card via PP.