Fantastic question. Hope some of the regulars in the AMA threads will chime in, they certainly like to on the negative side it seems, so be interested to hear about all the great things they do. A few from me:

1. Carry my clubs card so if I'm at a local park or field and someone sees me flying, I can hand the card to them and invite them to the club.
2. Land the plane, then show the plane to them, answer any questions. Go over the safety protocols we adhere to, and explain the basics of RC flight
3. Let people touch and experience the plane, buddy box if possible.
4. If I'm at my club and flying, and someone from the public comes to watch, show the around the club and invite them to ask questions. Again, buddy box them if possible
5. Proactively search out all types of Scouting clubs to come to the field, magnet school classes focused on science/aviation, and summer camp programs.
6. Set up tables at local events, schools, libraries, fairs etc to promote the club and the hobby.
7. Partner with middle school/high school science classes involved in the Science Olympics (free flight/rubber band powered planes).
8. Donate annual subscriptions to Model Aviation to all town libraries and middle and high schools.

Those are some off the top of my head, be interested to read about others and what they are doing.