Some races will have a dinner the night before. At the dinner, you will usually chat with others at your table and enjoy the evening. Don't eat much, however. Many assume, mistakenly, that they must eat a lot of food the night before. This is actually counterproductive. It takes at least 24 hours for most of the food you eat to be processed and useable in a race - usually longer. There is nothing you can eat the evening before a race that will help you.
But eating too much, or the wrong foods for you, can be a real problem. A lot of food in your gut when you are bouncing up and down in a race is stressful. A very common and embarassing situation occurs when the gut is emptied to relieve this stress. While you don't want to starve yourself the afternoon and evening before, the best strategy is to eat small meals and taper down the amount as you get closer to bed time. As always, it's best to have done a "rehearsal" of eating, so that you know what works, how much, when to stop eating and what foods to avoid. The evening before your longest run or walk is a good time to work on your eating plan and replicate the successful routine leading up to race day.