Im back on day three now but when I was in full flow before i packed in, I used to just drink water, very cheap night, just keep thinking of the greater good at the end of it all and dont give in.
drinking alcohol while on sole source is apparently very dangerous. i havent been out for 4 weeks since i started the diet because i find it easier to avoid it completely rather than go out and be tempted.
when i go round friends houses i take a can of coke zero (not officially allowed, but i can stay in ketosis if i have a few cans a week) so you could try that? good luck.