Drinks are very important. Alcohol is empty calories and can also give you the munchies so a double whammy really! Stick to spirits rather than beer, lager or wine and mix long with low cal mixers.
Tea and coffee have caffiene and can cause some water retention.
Full fat soft drinks like coke etc has a lot of calories and sugar and if you don't count them into whatever plan you are following they can be a real wrecker.
Water is the most important. You should aim for 1.5-2l per day. It doesn't have to be plain water, you can add no added sugar squash, flavoured water or herbal teas all count towards it.
Personally, I used to drink a lot of coffee and diet coke. I swapped this for one coffee in the morning then I have 2 cups of green tea and a litre of flavoured sparkling water. The sparkling water is cheaper than other soft drinks and I find it taste much nicer