I used to work for a top strategy house that would wheel out the drinks trolley each Friday evening. In principle, this sounds like quite a nice gesture. However the reality was very different. It was effectively a ploy to keep people in the office for a few hours longer. "Great", I would think to myself every Friday at 6pm, "after 80 hours in the office that's just what I need - feeling obliged to spend another 3-4 hours 'socialising' in this place". And just to clarify, slipping out early wasn't an option - this place had a 'collegiate' atmosphere and to do so would have been career suicide.
The other type I used to love were the events they would organise on Saturdays. I'd be thinking, "this is my personal time, guys - why are you organising work events on a Saturday??". I could have been out mowing the lawn, taking my kids to a theme park, doing a bit of sport, catching up with friends and relatives, but no - I'd be pretending to enjoy some kind of 'business game' in a sterile air-conditioned conference room or similar. Other people thought the same as me, but we were all too afraid to speak out back them - there was a bit of an 'anxiety' culture thing going on.
So, my advice? Simple - organise the event during work hours!