How should I make the Harry Potter and the DH Part 2 premiere(3D) more enjoyable without any distractions?

It's going to be late and I don't want to be drowsy so I was planning on drinking a caffinated beverage aproximately an hour before the show starts. However I did my research on caffine and it is a diuretic so that might cause me to have to pee. Also another concern is that I will get a headache from watching the movie in 3D. So i was planning on bringing ibuprofen in case. I also read that caffine assists with painkillers so that is always a plus. Anyway I'm just trying to make the experience enjoyable. I cannot afford to spend the last time I will ever be seeing Harry Potter on the big screen feeling cruddy and miserable. I do not care if I sound paranoid because Harry Potter is kinda a big deal for me. So any advice? I'm camping out in a tent in front of the theatre so I will likely have a headache anyway. So what are the dos and don'ts? But hey, maybe I'll be so emersed by the awe of Harry Potter that it wont matter. Btw I already bought my ticket so watching it in 2D is out of the question. I love 3D, this is just for precautionary measure. Opinions???