Kids Party Or Minefield?

Remember when you were a kid? How much did you love yourself a birthday party? Games, junk food, music- what's not to love? We used to have so much fun and that was when kids parties were nothing more than some fairy bread and a pass the parcel or maybe a pin the tale on the donkey. Ahh simpler times...
MM's party is this weekend and will consist of a Cars2 theme (and just so you are also in 'the know' Cars2 is very different to Cars and you do get told off for mixing them up). This means that there will be Cars2 'scene setters' everywhere (read- large posters of Cars2 characters), checkered (like race flags) table cloths, rediculously overpriced Cars2 party gear such as plates, cups, party hats etc. Even the bouncy castle has Cars characters on it (this could be an issue as they have not yet made a Cars2 bouncy castle). There will also be face painting and a giant 3D cake.
I have been planning his party for a few weeks now but in my usual fashion have left the menu planning (if you can call it that for a kids birthday) to the absolute last second. I was thinking 'kids birthday- easy we'll have some sausage rolls and party pies and maybe chocolate crackles and fairy bread. Done. Easy.' But then I thought about it. Can you really get away with that these days? I think of all the different kinds of parenting out there now and then there are the allergies. What about the kids who aren't allowed to eat junk food? Or are Gluten or Dairy free? I am I supposed to cater to these kids too? Should I have put out a 'Dietry Requirements?' card with the invitations?
I feel like I am walking through a minefield here. HELP!!
What do you do for food at a kids party? Are the classics still ok? Or are there new rules?