You`ll get plenty of diferent ideas but this works for me. I try to race 10k on the sunday before then have a rest day then a gentle 4 miles, rest day, easy 3 miles 2 rest days. As for fuel general healthy eating no greasy fatty foods. On the night before I have a baked potato with tune salad and in the morning a bowl of porridge and plenty of fluid intake. I don`t take any gels and just water on the day does it for me.