Drinks, snacks and good jazz?
Where in OC is this combination available? Good cool classic jazz and vibe are most important. Good drinks and snacks are less so. Does this exist in OC? If not, what about Long Beach, or LA?
Can't help w/ OC, but in L.A., there's Vibrato on top of Beverly Glen (elegant restaurant owned by Herb Alpert, good but expensive food, excellent jazz, nice bar). Catalina in Hollywood is classic, great jazz; not so great, but acceptable food (opt for simplest, least expensive dishes) and fine drinks. Also in Valley (on Tujunga) is Upstairs @ Vitello's for good jazz, tasty pizza, drinks. And in downtown L.A., recommend Blue Whale for cool ambiance, terrific jazz, often draws a younger crowd, a favorite of young up-and-coming musicians. No traditional table service, but tasty snacks and a solid bar (and lots of food choices in area as well)
Not sure how you define "cool classic jazz" - swing? be-bop? fusion? something else? But the Tom Kubis Big Band plays at Don the Beachcomber in Huntington Beach once a month (I believe it's usually the 4th Thursday of each month). Can't say much about the food, nor the vibe (faux Hawaiian/Polynesian), but the band is awesome - they're all top session guys. They feature a different outstanding high school musician every month, and Kubis's daughter's trio sings with the band as well. $15 cover, and it's almost always packed.
You could also try Spaghettini in Seal Beach. They have live music almost every night, but I think it's primarily smooth jazz.
Steamers has good music, but JAB isn't kidding about the close quarters. They'll also make you share a table with strangers if there is a not-full table.
As far as LA goes, as others have mentioned, the Baked Potato and Catalina Bar & Grill are two of the most famous places. They're the kind of place you buy tickets for in advance.
I haven't been in years, but Blue Café in Long Beach wasn't bad last time I went there. The main room downstairs was loud and crowded, with a wannabe blues rock band (think Blueshammer from the movie Ghost World) playing, but the upstairs lounge had a jazz trio and pool tables. Young crowd, but the music was good.
Is the Jazz Bakery back in business yet?
Looks like Strand House in Manhattan Beach has jazz on Sundays in the Strand Bar. I have not been yet, but the location is certainly great.