Credit card companies seem to have enough money to pay airplane company something for frequent flyer miles. There are also cashback programs.
I think the credit card company gets something like 3% of the money you pay for transactions. Maybe it would be possible to have a credit card that pays automatically 1 or 2 percent of the purchase price to a charity.
It might be very high leverage for someone in the effective altruism movement to facilitate the creation of such a credit card. The card might be default move the money to GiveWell recommended charities.
Credit card companies don't have the best PR and I think there a good chance that they would welcome a project like that.
You can already get credit cards that donate some fraction of the money to charity. I expect the marginal PR gain from one of those charities being GiveWell-recommended would be pretty small.
The actual leverage of creating such a credit card would of course depend on uptake, and for an individual effective altruist, it would likely be better to find a credit card with a good cashback rate and donate the cashback, rather than using a charity credit card with a probably mediocre or bad rate.
'MIRI' works in the search field when electing a charity to get 0.5% of your https://smile.amazon.com purchases.