+Do not try anything new on race day! + How many times have you heard it?  Whether it is shoes, shorts or breakfast... stick with what works.  How do we know what works?  We practice (rehearse) everything during our long runs: apparel, nutrition, hydration, lubrication...everything.  Marathon or Half-Marathon race day should be well rehearsed.  One of the biggest items: hydration.   Nothing can derail your race like stomach issues.   It takes some experimentation but planning a race day hydration strategy should be as important as completing your long runs.  Dehydration is a danger but so is too much water.  Another sneaky culprit is drinking a sugary sports drink that your stomach cannot process.  This leads to stomach shutdown which leads to... dehydration.   Worried?  Good because you need to figure out what works and stick to your plan. 

Here is a very good article on race day hydration from Matt Fitzgerald at Training Peaks:

Hydration Strategy

Ya Gotta Believe,  Coach Kevin