You've only just started so you may not be fully in ketosis. Once you are you will not feel hungry. And it is possible to go to parties, you drink bubbly water! And you have your bar or shake or soup just before you go and you say no to food that is offered to you. I can't say it isn't difficult but it helps if you go with someone who is supportive and then you can collect food and then give it to them. Likewise with cake. you can take a piece and then make your excuses and put it out of the way somewhere. It's not a waste of food, someone else is likely to have it and even if they don't the food was allocated to you and you decided to leave it.
I did a birthday party within days of me starting and was offered cake and champagne and I employed the above strategies. I have another to go to this weekend, and I will do it again.
I just figure that though I love my food, this is not forever. I also have my own birthday in 2 months and I already know I will not be having cake! I am not that worried as I hope with losing lots of weight I am going someway to ensure that I have many many more birthdays in the future. However, I could not miss Christmas. But I also do not want to undo all the good work, so it will not be the case that I eat every mince pie offered or eat large lumps of Chrimble cake. But I do want a roast on Chrimble day and if I manage to lose 4 stone in total by then, I think I will deserve it. It will be worth it, don't buckle now! =)