When I tip the driver in a delivery I literally just give them cash when they deliver (and only if they actually arrive with some promptness, not if they come half an hour late with a cold pizza).
It’s a habit I got into when living in the UK because there, like in the US, lots of companies just take the “tip” money and keep it if you tip whilst paying with card.
Granted, I like to pay stuff with cash, both for privacy reasons and because it has actually been shown that people in average spend less if they pay in cash (something to do with the feeling of giving something physical away), so I almost always have some cash to pay and tip.