When friends give me free food or drinks, I usually tip the full cost of what I was given. So if you gave me an $8 drink, I would tip you $8.
This still benefits me in that I don’t have to pay that $8 plus another tip, but I’m wondering if there’s an expectation or standard that would save me some $
Sometimes this one place gives me $20 of food before closing when I only intended to spend $5 so the upsell kinda hurts
The expectations will probably be different between cultures but personally, nothing. It’s a gift after all, giving them money for it would make it a business transaction. Of course, when there’s an opportunity, I’d give out some food or drinks to my friends as well.