For everything less than 15 km, you really don't need any special preparations compared to a normal training run of the same length. Neither for the day before, the hours just before the run nor during the run itself. If the run is in the morning, I usually try to avoid anything excessive spicy or greasy the evening before - this is just to make sure I don't feel bloated during the race...
Training wise, I usually don't run the day before a 5km race, two days before a 10 km race and 3-4 days before 15 km. Just to make sure I'm fully rested...
You will hopefully run a bit faster than during the training passes, so you will probably want to drink some water and eat some fruit and salty nuts after the run. This will help you recover from the run quite a bit faster.
EDIT
For HM and longer, I have a different pre-race approach by necessity. I cannot run that long as fast as I want without proper preparations - not that I will not complete the race, but afterwards I will hurt for a couple of days if I just take the 15 km approach.
The HM preparations mean more carbs (pasta and white bread) and absolutely no alcohol the last two days and relatively little protein and fat the last 12-18 hours. And of cause plenty of to drink the last week... On race day, I have less cerials in the morning than usual and some apple juice instead. During the race, I drink a couple of cups of Powerade and nothing else. After the race I try to make up for the lost calories with chocolade, fruit and beer :-)