Cut your toenails at least 3 days before your race.
I can't stand when I can feel my toenails when I run. I cut them a few days before a race and then I'm ready to go.
Drink your water.
This is obvious to most, but your hydration days before your race is just as important as race day hydration. A 5K is considered a sprint, so there are often no water stations. Consider planting your own water bottles or having a friend cheer you on with a drink at the halfway point.
Check the weather so you wear the proper amount of clothing.
The fewer clothes you wear, the faster you go, but if you're frozen you won't get anywhere. I guess there is a reason for short running shorts. I will be wearing my knickers.
Don't overeat the night before.
I feel better in the morning when I don't eat past 7 pm the night before. Eat a normal meal that isn't to heavy, greasy or overly fibrous. If you need to carb load for a longer race, eat more at breakfast and lunch.
People recommend eating before a race, toast with peanut butter and a banana, for example.
For a 5K you might not need to eat much as long as it starts early. My race is at 10:30 am, so I will be eating breakfast around 7 am to give me some time to digest. I might get a GU just in case I don't feel like eating in the morning.
Rest the day before
No exertion except stretching or walking.
Get a good nights sleep.
Set a curfew and go to bed. ZZZZZZ
Do what you've trained to do.
Don't try to switch things up on race day. Don't wear new shoes. Don't try an energy drink you've never had before.
*****Do have fun. That's what it's all about.