From left: Anita Pallenberg and Mick Jagger, living la vida coca.
Studios used to prepare short, behind-the-scenes promotional featurettes advertising their upcoming films. These featurettes could then be played between double features or distributed to TV stations for free play.
Here's one advertising Mick Jagger's participation in Donald Cammell and Nicolas Roeg's bizarre gangster fantasy PERFORMANCE (1970). You'll see Mick Jagger preening on set and playing the patch-bay of a Moog synthesizer while an ultra-square narrator drones on, saying things like "the synthesizer is an electronic device capable of producing any sound in the world."
The video cannot be embedded because of the uploader's settings, but you can view it here. And by all means, if you haven't seen PERFORMANCE, check it out. It's crazily indulgent and fascinating.