Odds are that you have put in a tremendous amount of work to prepare for this epic race. Early mornings, long runs, speed work, strength training, food preps...this is not including the previous years it took to qualify for the race... the amount of work to prepare for a race of this magnitude is maniacal.
The worse thing you can do is over-train the last 2 weeks before the race. The work has been put in, the fitness has been built, it's now time to soak up all of the training that has been completed over the past few months (even years). Allowing the body to fully recover while keeping the legs sharp and tuned up is a tricky concept. Here are a few points to consider...
*I recommend decreasing mileage the last 2 weeks 30-50%. This range is broad and depends on the fitness level and experience of the athlete. Some athletes can get away with and still perform with a small decrease in miles, while others respond to minimum (but focused) miles and more recovery leading into a big race. But both individuals will still drop miles. Find what works for you. As you are completing a workout, just remember, more is not better. This is the time for pure quality training. All miles should be focused and specific to your goal pace. Miles should be low enough to instill adaptation but not too low where your legs become flat. If you topped off at 16x400s, then 8-12 days out from the race, drop it to 8x400s right at the recommended pace. Still do a warm up and cool down like normal. Just decrease the main set volume. You want to be leaving these last few main workouts feeling sharp, fast and in peak form. Don't go to pure exhaustion. Also recognize when your body may be extra fatigued, stressed and overtrained. On this day, I recommend a DAY OFF or a very light shake out. Listen to your body and be a smart athlete.
*Sticking to your core routine is critical to having a successful race. 2-3 days per week should be the guideline. 10-15 minute sessions keeping the core engaged and activated will help your body stay primed and feeling strong. Planks, side planks, deadbugs, birddogs and farmer carries can be done all the way leading up to the race. Stay away from loaded lower body work and stick to bodyweight exercises. Upper body strength can be moderate but move to bodyweight movements the week of the race. Blood flow is blood flow and creating this throughout the entire body makes for a better race lead up.
*Nutrition is where many athletes screw up. First of all, this is not the time to go on some calorie restrictive diet. Be wise here. You definitely need a nutrient dense intake. Lots of dark leafy greens, fish, lean meats, fruits and other vegetables and whole grains/complex carbohydrates according to your specific guidelines. Everyone is different. Starting on Friday before the race, increase your carbohydrate intake 10%. So if you normally are consuming 350 grams of carbohydrates, aim to hit 385 grams. Do this again on Saturday and Sunday. This will help top off your glycogen tank to make sure your muscles are full and prepared to work. YOU SHOULD NOT RANDOMLY CARBO the night before. That will just lead to an overactive gut the night before your race. You can consume a carbohydrate dense breakfast the day before, but from lunch onward, eat just enough to fill your stomach, not so much you get bloated.
*Water and electrolytes should be the focus on liquids. Balancing in electrolytes throughout the week leading up to your race will keep your sodium levels adequate. DON'T JUST DRINK A TREMENDOUS amount of water the days leading up to your race, as you could flush out your sodium, which creates a very low blood sodium level, called hyponatremia, which can be detrimental to performance. Stick to your normal fluid intake, just be a bit more cognizant of what you are doing.
*Lastly, visualize your race. All the physical work has been done. But many athletes lose it mentally the last few days before a race. Set realistic goals based on your training times. Mentally put yourself through the race. I have athletes write out a detailed race report 2 weeks from a race so they can then "run" through the race periodically as race day approaches. Write out what time you will wake up, what you plan to eat at what time, when you will arrive to the race, what will your warm up be like and when, what pace you plan to go out in, what nutrition will you eat and when, what you will stay focused on, and how you will finish. Sticking to this blueprint as best as you can makes for a better race.
Be confident in what you can do. Believe in yourself.