I’ve been invited to a colleague’s birthday party in a couple of weeks time. I’ve known her for about three years and we’re friends but not close friends. She’s having a barbecue in the garden so it’s all fairly informal.
I’m not sure what to do about presents - should I buy her a little something and a card as well, or is it acceptable to bring a bottle and leave it at that?
It’s been so long since I’ve socialised that I’ve forgotten what’s expected! 
We’re all in our early 40s in case that’s relevant.