When most people hear the term "carb-loading", a big pasta dinner the night before an event comes to mind. However, this is not the best way to load your glycogen stores (glycogen is the form carbohydrates take when stored within your muscles). Research has shown that you can build-up glycogen stores better by eating 70 to 90% of your total calories from carbohydrate for 2 to 3 days before an event. That means that you should still aim to eat roughly the same amount of training calories but aim to eat more of those calories from carb sources.
For example, during a normal training cycle, runners should be aiming for about 60% of total calories from carb. So, if you normally eat 2000 calories, then 1200 of those 2000 should be coming from carb, or about 300 grams. For the 2 - 3 days prior to a longer race, increasing to 70 - 90% of calories from carb would then be 1400 to 1800 of 2000 calories, or 350 to 450 grams of carb.
Great carbohydrate sources are pastas, rice, cereals, breads, dairy products such as yogurt (if you eat dairy), fruits, and starchy vegetables. As far as fruits and veggies go though, just for the 2 - 3 days before the event, you may want to consider limiting or avoiding beans and very high fiber/roughage types of fruits and veggies to avoid distress.
Practicing carb-loading 2 to 3 days before your longer training runs is one of the best ways to fine tune your fueling plan for a race. This gives you plenty of time before the actual event to figure out what works for you. We invest so much time training our bodies to handle the miles, and should be investing the same amount of time into training our guts. Consistently practicing your fueling before, during, and after longer training runs is one of the BEST ways to avoid GI distress during events.