Logging out of the site and logging back in, or changing your password, expires your session cookies! So if you've changed your password, you're good.

Yeah, theoretically, if you made a credit card payment during the time the leak was happening, there's a small chance that your details may have been exposed. Personally, if I'd made a credit card payment during those days, I wouldn't be worried about it at all, but if you're concerned, just keep an eye on your CC statement for a while for any unfamiliar charges!