At 5 dpo it's unlikely that the fertilised egg will have even implanted, let alone anything else. I always have the odd drink when I'm in my 2ww, otherwise you're just putting your life on hold. I'm sure a couple will be fine. If you're eating too you should be able to have a few more. If you're worried about lasting the night - have spritzers or shandies so you can be seen to be drinking the same as others, but in reality, you're only having half (if that makes sense).
I don't smoke, eat fairly well and am reasonably healthy, I'm not going to deny myself the odd drink until I get that bfp!
PS we went out on a friend's 40th and they were unaware at the time she was pregant (a day late and she wasn't trying at the time) and got sozzled - she went on to have a hulking 9lb 10 lovely, healthy boy.