Hi Ann,
Well this is going to sound like a cock-eyed answer, but yep - drink loads of the stuff itself!!
I had a write-up all about the science of water within your body cells saved on my old PC, but I have no idea where it is now!
Anyway, it got me a great grade in Uni when I did my chem degree
Anyway, to cut a very long & involved chemistry based lecture short... your body often retains water when it thinks it is starved of the stuff.... so if you increase your daily intake, it can help banish retention totally. Once your body realises that you're giving it what it wants, it will let go of the excess.
I used water extensively as a diet aid - 6 litres a day was the maximum & helps to flush the fat molecules out too - the only drawback with that was the spots - I guess the junk has to come out some way
I'm not suggesting that you start drinking 6 litres a day though!! But if you up your water intake over the next few days, you might well find that although you'll have a lot more loo trips, you'll also lose a few centimetres too - which could help you with your outfit.
The sodium imbalance can also be brought back into line by drinking plenty of water too - it's a funny thing, water.
Good luck - and have a lovely time xx