Look, I work on my friends cars all the time and dont expect anything. And I have a good friend that when I work on his car he brings me tacos and im happy. A good friend dont want money for stuff like that. Just return the favor and buy him a good meal or some beer/booze depending on what he likes. Help him work on the car. Hell my friend grabs all my tools for me when im doing work and that saves alot of crawling out from the car. 

