Donating miles to Make-A-Wish is easy, Pratt notes. "Just go to our website."

Donations increase in time of disaster

How common is the practice of donating credit card rewards or frequent flier miles to charity? It's hard to say.

"We don't break out numbers in terms of how many people donate to charity," says Fish, of American Express.

Capital One doesn't share specifics either. "But there are small percentage of cardholders that use their rewards to make donations," Sahni says.

Card members like having donations as an option, Fish adds. "It is a way to help without having to spend extra money on their part."

Charities do find that donations of credit card rewards points increase in times of international crises such as earthquakes or hurricanes. "That's likely because during times of crisis/disasters it is something that it more top of mind," Fish says.

Get a receipt but not deduction

When you donate your unused or unwanted rewards points, you should get a receipt. The sites generate them automatically.

You need to check with an accountant to see whether your donation of rewards points or miles is tax deductible. It likely is not. "But if you don't itemize your taxes, you might not care," says personal finance columnist Liz Pulliam Weston.

To be sure to get a tax deduction, make your donation with cash or check. Ironically, if you make the donation with a credit card, you could earn more rewards.

Pratt says when she donates her credit card mile rewards - tax deduction or no - it's worth it to her because she knows what it means to the children and their families they help.