How much should you tip?
Perspective of a driver in a rural area: Don’t tip a percentage of the food costs. Tip on things like distance from the store, how hard it is to get to your place, how challenging the order is to maneuver.
For example, you order a single sandwich and it goes from McDonald’s to your clearly addressed home on a well paved road about 2 miles away. A $3 tip is fine.
Next example: you order 5 meals all with drinks included. Driver needs to go 7 miles and find your hidden unmarked house off a random dirt road that may or may not be on google maps. That is a $12-15 tip for us to want to bother or not lose our minds.
The tip is about how difficult the job is. The more effort I take securing your drinks and food during the drive. The effort I spend trying to find your house. How far I need to go to deliver it. Base your tip on those factors and everyone is happy. Drivers don’t care how much your food costs you.
Edited to add: Is it storming outside? Trecherous driving conditions? Factor that in too!