My grandma used to tell me: “you need to eat in order to run all these miles” Also there is this old saying: “your body needs energy!”. Bullshi!t!
During your training, your body adapts its metabolism and improves its ability to burn fat and turn it into energy. After a certain period (about 45 minutes to 1 hour), your glycogen stores in your muscles are depleted and your body starts to take energy from your fat. That is why you need to (1) not overeat to prevent stomach aches, (2) be prepared to consumes food on your run to get immediate energy and (3) work on getting your body used to transform fat into energy.
For sure, you will need enough fuel to put your ass to the finish line. But overloading your stomach with plenty of sugar (because honestly, most carbs are just sugar) will rather trigger GI issue, bloating and eventually make you sick in the middle of the race. On top of that, carbs (and sugar) are rather factors of diseases and contributors to get diabetes. There comes the question of why you run: if you run to be healthy, getting your body be used to a ton of sugar is just counter-productive.
Your grandma can still argue that you still energy before a long run but in fact, as race day is coming, your training is reduced and, if you do not change your diet so much, your body get (and store) more calories. What matters more is to be sure that your body is well healed and rested. Make sure you get enough sleep during the week before the race.
On the other hand, you need to get enough energy during the run, not before. Your glycogen store (long story short: where your muscles keep the energy before taking it from fat) can last for about an hour. So, make sure you get energy during the run. Energy bar, gels or anything else you want and are able to handle. The idea is to maintain the sugar level within your body rather than playing with it like a roller coaster. Finally, selecting the food you can get during your run is something you have to try while training to avoid any inconvenience on race day. Recently, a trail-runner drops into a course in La Reunion (La Diagonale des Fous) because he did not store his food in a fridge. He got food poisoning, got sick and eventually dropped.
So what should you eat before race day? Same thing as you are used to. Stick to food you can easily process (vegetables, soup, etc.) and do not overeat so that you avoid any GI discomfort and any sleeping issues before race day (an overloaded stomach can trigger discomfort when sleeping). On my side, I eat the same thing as I do every day (mostly peanut butter toast for breakfast, lentils/bean soup for lunch and tomato soup with peanut butter toast for dinner). If I am outside and hang out with some friends, I might take something else (even a burger) but it does not really matter because I stick to healthy rules all week long (which is most important than eating crap all week and just stay healthy before race day). Again, the most important is to stick to healthy choices most of the time and having some exceptions from time to time.