Assuming it is a morning race (9 am or earlier), I don't eat anything for a 5k or 10k. I'll make an exception if I have to be up three or four hours early for the race, but if I can get up at 7, and the race is at 9, I'll just eat afterwards.
It sounds bad, but I have found that junk food (notably twizzlers, but oreos as well) sit well in my stomach when consumed before a long run. On my last marathon, I had a Boost an hour and some before the start, and didn't have any GI issues. (I have tried bagels, toast, etc - but all have given my significant GI issues, sometimes during bad times in the race.)
Just try different things - you'll find what works for you.