I think it depends on how often you socialise. If you go out every day, then clearly you need to work out how to do it. But if you go out once a week or less, then I think a beer or two and a not fantastic meal would be okay, provided you think of that as your treat for the week and be really good the rest of the time.
I reckon, so you don't feel left out, you should definitely have at least one beer. Maybe a light beer? Calorie king reckons beer has 72 calories/200mL glass, and light beer has 56. If you plan, you could definitely fit those in, especially when a glass of coke has 86 calories, and lemonade has 84. (Course, water or diet soft drinks have much less, but who says you have to ONLY drink them?) Drink a beer, then switch to water or diet soft drink.
As for the food, I'm in a similar situation most nights during term. Most lunches even. I live in a fully catered university college, so I can't cook for myself. Which means I have no control over what goes into my food. No low fat alternatives, no extra veggies, nothing. How do I get around that? (And I was loosing far more weight there than I am at home.) I gave myself a couple of sensible rules: Nothing deep fried, including chips. No pastry. No dessert. Always get veggies, unless they're really gross. I don't have to eat everything on my plate if I don't like it. No seconds. So, as long as my meal fit into those guides, I didn't worry about it, cos there was nothing I could do to change it, short of moving out, and there was no way I was gonna do that! I reckon you could adopt a similar idea. Like, when you're out, steer clear of the fish and chips, or the pies, but do get a hamburger or a steak or a curry or something. They're not that bad, especially if you watch yourself earlier in the day.
But really do keep up with the socialising. After all, if you've got no friends left, who's going to tell you how pretty you look when you're at your goal weight? Not to mention life would pretty much suck without your friends.
Hope that helps!