To get ready for the exciting day, may I recommend three things.
Wake early and prepare and dress in your running clothes (or better still put on your already prepared running clothes from the night before).
Eat light an easily digestible meal low in fibre such as a banana and piece of toast with honey, or whatever you know is good for you. Give yourself plenty of time to sit on the loo for effective toileting!
If you are sick, consider your goals. Don’t run if you have a fever or some undiagnosed illness that will endanger your health if you compete. If you are a bit crook, revise your goal to an easier effort. Maybe a ‘social run’ :-)