If I'm stopped for running a red light or a similar minor traffic offense, and the officer asks to search my car (or even myself), should I let him?

No, no, no.  You should be polite but clear that you do not consent.  If they smell marijuana, then they can search without consent.  

We recommend that clients watch the video "Busted" online to see an example of how tricky the cops can be with this business, as well as the short video by Harrisongburg, Va attorney Bob Keefer called "Never consent to any searches! II."