Pilot. It gets you all the basic background, and the rest of the series will be hard to understand without it.
Out of Gas. Flashbacks give you some background on the rest of the crew.
Object in Space. The bounty hunter (whatshisname?) makes an appearance in the movie, and it's just a really great episode.
If you have time for a fourth, I would think maybe War Stories or Heart of Gold. You might just want to see which episodes your friend already likes, and go with something like that, but War Stories adds some background, and is a damn fun episode ("I thought God had something to say about killing?" "Indeed he does, but he's a little more open on the subject of kneecaps."). Heart of Gold is just one of my faves, I'm a big fan of the 'Good guys find those that need help, fortify a position, and take on all comers' kind of setup. It's like Seven Samurai (and therefore the Magnificent Seven) in a one hour TV show.