My favorite idea for a solar cooker that's easy to transport and set up is the "Sunbrella". Essentially it's an umbrella with a highly reflective underside that, when open, creates a parabolic reflector. It's light and it's compact when folded.

Unfortunately, the weak link in that idea so far is the reflective surface. Highly reflective surfaces tend to crinkle and in other ways become less reflective as they are continually folded and deployed.