First off, have you gone to a restaurant whose only seating was in booths, and rather snug ones at that? If using a pocket carry setup, could you draw and present your firearm without having to stand up? Is a belt or shoulder rig any better? Is it possible to get under the table? Should you always try to sit towards the aisle side of the table, if you are the group's "designated shooter" for the evening? Probably not such cut 'n' dry answers, in many cases. Not something to lose sleep over, just food for thought, no pun intended.
Have you ever done an "ID scenario" at the range? This requires a partner, so you can set it up for each other. Have one person face away, while the other is downrange putting props--such as toy guns, knives, lighters, cameras--on the targets. When the drill starts (let the guy downrange come back first, please!
) turn around and sort out good guys from hostiles by what the targets are "holding". It will slow you down, making you think and perform at the same time, and perhaps force some lateral movement. These are good skills to have, and may help save your bacon in a real situation.
There's a bazillion other firearms sites out there with scads of keyboard kommandos aboard, just waiting for a topic like this to boost their post counts!