Pubs are usually okay, if they're decent. If you're at a carvery meat and green veg is a good option - but avoid anything like carrots, parsnips and cauliflower cheese (it will be full of flour) as well as the roasties. Gravy depends on how much you're having - a little bit to flavour up your veg would be ok if you count 2 or 3 carbs for it, but remember that the thicker the gravy, the more flour will be in it. Really thick gravies can be high in carbs.
Most pubs will do some variety of steak, though, and let you skip the chips in favor of a salad. Gastro type pubs should do a range of salads with different meats or cheeses, and you'll often find scallops and prawn dishes. You can always have two starters if they suit you better.
As for pud - have something when you get home. Sugarfree jelly and cream, or cream with a tiny bit of cocoa powder and splenda mixed in, or a cheesecake of Philly, splenda and a squeeze of lemon - lots of other recipes around but it's best not to get too complicated. Or grab an Atkins endulge bar from boots (not ideal for phase 1 but ok if desperate on occasion).
I know it's tough not eating your usual, or the same as everyone else. But potato and pudding won't taste as good as you remember, and they'll slow your loss for a week so you'll in effect be restricting yourself longer if you have them. All the puddings and anything else you fancy will still be available when you're on maintenance and can have things like that now and then.
Good luck!
Edit: why not check if the pub has a website with a menu on? Lots do.
