how much do you tip those who deliver food?

<p>Son worked at a sandwich shop two summers. I hated when they assigned him to deliver. The shop charged $5 to deliver but they did not give that money to the driver. They figured they are already paying him his hourly wage. I think the owners took advantage of the young employees or the employees whose english skills were lacking. I finally told my S he could not take the car to work. If he didn’t have the car he couldn’t deliver. It was my car and my gas. He rarely got tips since people felt they had paid for the delivery. The worse offenders were the tech firms in the area that would order large orders and only be charged $5 but expected S to carry everything inside to the conference room.
The only place that delivers to my house is Dominos and a local pizza place. We rarely order since I prefer the another pizza place. For Dominos I usually give 3 bucks.
Walk up places I rarely leave a tip or just my extra change.
Where I never know what to tip is the local place where you wait in line to order and get a number. The wait staff delivers the meal to your table on real plates and silverware. What is an appropriate tip in this case? Not 20% since you have to stand in line to order but 10 or 15% or a few bucks depending on the order?</p>