Norethisterone is great, I seriously recommend it. I've had it a couple of times and it didn't have any side effects for me plus I was able to get it on prescription, not sure why another poster had to pay for it? So go to the doctor and ask for that
How often do people leak anyway? I only ever leak at night or if I've been really lazy and not changed for too long in the first two day. You should be fine by just doing what you usually do - it really doesn't sound like it's worth taking a pill for just one night. You'll be fine, periods aren't a big deal...
If you wear a tampon and make sure you insert it correctly, and change it every 2 or 3 hours you should be completely fine! If you're worried about acne I wouldn't take a pill or anything, there's no reason why a tampon should leak unless you just don't change it for like 6 hours or something
Have a go at using a tampon and if you still feel concerned, use a towel at the same time - it gives you a great peace of mind. Although you may feel awkward at first, they are really handy and you get used to them within like two hours.
Apparently this isn't an issue for most people, but when I was on Norethisterone I spent vast proportions of the day with my head over the toilet trying desperately not to throw up and could barely move because my splitting headache was that bad... won't happen to everyone, but if you get side effects with Norethisterone, they are pretty difficult to cope with.
The combined pill can help with acne and you'd be able to delay your period for prom and settle into a regular routine. Then if another similar situation came up, you could just run two packets together and you wouldn't need to worry about it.
I would also recommend asking for the tablet to delay your period, because then you won't have to think about it at all. If not, try Tampax Lites, they are less absorbant than regular tampons, but thinner so easier if you aren't used to them. To be doubly sure, you can wear a pad as well.