to my knowledge the rule is: if you brought it, you can take it--in fact, i read the actual laws about alcohol in restaurants without a lcense and it kinda surprised me how strict it was about how you couldn't even have open wine in the kitchen for cooking, and other pretty harsh restrictions. apparently no one pays attention to that. but anyway, yeah, if you bring it, you can take it. if you buy it, you can't. ← I've been to a few restaurants where I bought it and was allowed to take the unfinished bottle home. Maybe they were bending the rules.