A number of famous personalities appeared in extra and very minor roles on the Rebel Base in Empire Strikes Back. Movie star Treat Williams, visiting the set to see his friend Carrie Fisher (married to Paul Simon at the time), got into wardrobe to be an extra - it's unlikely he was even paid, he just showed up to hang out. A lot of people get jumpy claiming to see Treat Williams in the movie as this or that rebel snow soldier, but it's very likely his scene just hit the cutting room floor. In the film itself, he remains unidentified.
Ralph McQuarrie, the brilliant science fiction concept artist who designed the look of the series, appeared on the base as a General. Appropriate, considering the magnitude of his contributions.
John Ratzenberger, better known as Cliff the Mailman from Cheers, actually had a speaking role, where he informed Princess Leia the base shield doors had to be closed with the approach of night. Decades later, when he was a well known actor, Ratzenberger was asked to reprise his voice for a video game.
