do my credit card statements act as my receipts for charitable donations since many contributions are online?

[RobertB4444]

You need a tangible piece of paper to be able to show the IRS to back up your donations.  Most of them would send you a thank you email that you can save and print if necessary.  

Your credit card statement may work if it says "GOODWILL DONATION" or something like that.  But if it just says "GOODWILL" then the argument is that you could have just been shopping at the store.  Take a look at your credit card statements with a skeptical eye and see if you would believe you.  If the answer is yes then they are a good receipt and carry on.

@Chris-3420