Coke and other fizzy drinks strip the body of calcium causing arthritis. It also has so much sugar in it that it turned a friend of mine into an insulin dependant diabetic (non reversible)
If you're on diet coke there are also a few horror stories written about it. link 1
and Link 2
There is nothing that can stop you from eating the snacks your friends bring into the house except for you.
You alone have to set your mind on reaching your goal, your friends care about their lives, you have to care about yours.
Read a few of these reasons why you should lose that extra weight, it might help you stay strong - Link
Another thing that might work is buying yourself a chunky ring or a big beady bracelet, so that everytime you reach forward to grab food you'll see this piece of jewelry and it'll remind you to Stay Away from eating Fat (don't tell anyone in the house what the jewelry means, it's just your secret code for yourself)