Oklahoma is about like Florida on this issue -- you can carry in a restaurant but stay out of the bar area (I think it actually stipulates no sitting at the bar while armed). Works for me. As for actually having drinks while sitting down to eat, the law is silent on that (as it should be). Get yourself out of line while armed and see what happens.
I think most of the states who disallow carry in places that serve alcohol have that in their law due to poison pills by the anti-gunners, who try to put road blocks in our way anyway they can.
I haven't noticed any restaurants in Oklahoma that have "no gun" signs, but then Oklahoma's concealed carry law (enacted in 1995) never said anything different than the above about restaurant carry. Around here it is mostly 7-11's and some banks that post no carry (oh, and most hospitals). But it isn't against the law to carry in these places -- just those places desire that you don't.