Yeh go buy a slimming outfit, you will see yourself better in the mirror and feel more confident, make sure you put on some make up, and do your hair, and that will in turn make you feel much better. Like mentioned, they will be very weary about parts of their own bodies as well. so just go to have fun! just go to catch up, you not there to catch a date or have a who's skinnier competition. If they are as judging as your head thinks that they are? Then they aren't friends. You will be your own worst enemy, and not having a good time will be down to you beating yourself up about the extra 30lbs or so.
Just do as much of what will make you feel great!