Remember this if nothing else...

Don’t let your diet deviate too much from what got you there in the first place.

In the days leading up to a race, many athletes, swimmers included, try to get a head start on their race day fueling requirements by consuming extra amounts of water, calories and sodium. This is completely counter-productive because the body is simply not designed to accept these excess amounts of fluid, calories, and salt. As one well-known sports scientist states, “When we try too hard to help ourselves we end up causing more problems that we resolve.”
Since the majority of athletes tend to go overboard with calorie intake during this time, let’s focus on that one aspect. If you hope to achieve the best results possible, in the days leading up to your competitions, don’t stuff yourself with extra food in the hopes that you're “carbo loading.” The time period for carbohydrate loading (i.e., maximizing muscle glycogen storage capabilities) has, for all intents and purposes, passed. In essence, carbo loading is what you did in the 0-60 minutes after all of your workouts in the weeks and months leading up to the race. That’s when the glycogen synthase enzyme—which controls glycogen storage—is most active, and that’s how you maximized and topped off your glycogen stores. Any excess food you eat in the days leading up to the race is either going to be passed through the bowels or, most likely, stored as fat (i.e. dead weight). Neither of those things will benefit you come race day.

Got that?

Simply put then... after each and every HARD training session or race event, eat yourself silly, fill your boots.
Eat less in the times you do easy spinouts or zero training.