like eveyone has said, nothing really canon, other than missions into russia or russia areas (gamekeeper) which is his special forces. and he's a paratrooper or whatever the official term is.
me, i've got this silly idea....there was a special on pbs last weekend on air force one and they menioned the guy that carries ''the football' a briefcase with all the codes to launch wwIII...now given that jack has said 'air force one and i go way back' i've had this image of him pulling that duty at some point in time. i don't know why i just do.
playing around in washington for a while certainly would account for his contacts, that and 20+ years in the service.
i don't think jack can fly, my only rationale for that, he doesn't wear wings. i certainly could be wrong but i thought once you earned em, you kept em. even if you technicaly aren't qualified to fly you are still a pilot and can wear your winge. jack doesn't.
this is all taken from
http://www.trickster.org/arduinna/sg1refmain.html
which is taken from the show unless stated as fanon.
its a great research page
USAF 66-789-7876-324
Has to have been in the AF for at least 18-19 years to make full colonel. (Joined in 1975, which puts him at as much as 24 years of service as of 1999, although probably 22-23 years because of his temporary retirements. As of Fair Game is wearing an AF Longevity medal with, apparently, three bronze clusters. This can't be right. The medal is for four years of service; each cluster represents an additional awarding. This would mean he's been in in the AF for at least 16 years, but less than 20, as of 1999.)
Has parachuted hundreds of times (Watergate) (is a master-level parachutist; see his full set of medals)
Joined AF at 18 (according to MGM press kit info): "When he joined the Air Force at 18 years of age, O'Neill proved himself to be an exceptional and gifted airman. Assigned to a special training program for covert operations/infiltration, he was trained in the skills of wilderness survival, special weapons and tactics, assassination, demolition, chemical weapons, the manufacture and detonation of explosives, and is a field expedience specialist."
Has resigned twice so far: once after Charlie died, again after returning from Abydos the first time. To have retired (with pension?), would have had to be in the military for at least 20 years already; if he joined at 18, he couldn't retire before 38 (which works out about perfectly, if he's 40 in first season -- which was just over a year from the first mission, which was shortly after Charlie died). Presumably could resign at any time, though.
Will be facing mandatory retirement from active duty after completing 30 years Total Active Federal Commissioned Service. Don't know how long he's been commissioned (although he was a captain as of 1982). Factor in breaks for retirement, he could have 10-15 years left. (retirement info, etc., from the Colonels' Information Handbook)
Recalled from retirement to lead the first mission to Abydos. (Stargate the movie) Retired again on his return, and was recalled again more than a year later to answer questions about the first mission and eventually to command SG-1, the SGC's flagship team.
Has served as official AF technical consultant to a tv show. (Wormhole X-Treme)
Pre-SGC Missions:
1982: Operation East Fly was a mission to retrieve a Russian agent named Boris from a house in East Germany. Members of the team included Captain O'Neill and Captain Kawalsky, under the command of Colonel John Michaels who was killed in action by snipers. (Gamekeeper)
Fanon has Jack serving in Viet Nam. This is impossible. Jack didn't turn 18 until 1975 (canonically born in 1957--Brief Candle), which was the year that all US troops were finally pulled out of Viet Nam. Even if he'd lied about his age to get in younger, we weren't still sending troops to 'Nam at that point. The "proof" given for this fanon is that Jack wears at least one Viet Nam medal. But, given the aired canon on Jack's age, this is simply a mistake. The two Viet Nam medals given were both given only up to 1973 -- Jack would have been 16 in 1973, and certainly couldn't have served in action long enough to have earned the medals--he would have to have joined when he was fifteen. (For specifics on the medals Jack appears to be wearing, see the Air Force descriptions: Vietnam Service and Republic of Vietnam.) Since prop canon is only valid in the absence of aired canon, this basically doesn't count. (Moreover, a closer look at the medals Jack and Sam are wearing during her promotion (Fair Game, third season, 1999) shows that she's not wearing the Air Medal -- which she earned a year earlier (Secrets, second season, 1998). So I'm looking at these medals as a guide, but not cast in stone.)
and this page has all the medals...though they do vary from eps to eps as the wardrobe folks sometimes forget who wears what
http://www.trickster.org/arduinna/sg1refmain.html#medals