My suggestion is eat a decent breakfast about 3 hours before your start time, I like porridge and wholemeal toast with a bit of jam but you might have different tastes. Your looking for slow release carbs really, forget about the protein until after the race. Also try and make sure you drink enough that you’re properly hydrated.
In the hour before the start sip a carbohydrate energy drink to top up your energy levels.
I also find having an energy gel 10 minutes or so before the start helps.
If the race is less than 60 minutes you shouldn’t need to worry about eating during the race, if it’s much longer then try and make sure you take on some more carbs mid race, gels or energy drinks are good for this.