Funny you should ask: I've been going over my SG-1 rpg stuff lately.
The 'typical' SG team is usually 4-6 members, with A team leader, heavy weapons specialist, language/cultural expert, and a mission specialist/science expert.
Since the SGC is a military organization, there isn't really alot of civilian team leaders or heavy weapons specialists, so the missions specialist,cultural or science areas would be the most likely place to have a civilian. But then you're going to have to figure out why the gov't is sending a civilian when they could just send some Air Force hot shot.
That's where the Daniel Jackson's and Rodney McCay's (on Atlantis) come in; they are specialists of such depth that no other substitute will do. But once you have a good concept (the test pilot is interesting, but hard to justify for more than a couple missions. But the SGC does find some really cool toys! )
_________________
"Yes, it's the Apocalypse alright. I always thought I'd have a hand in it"
Professor Farnsworth