Race day

Despite the race event being on one day, it actually extends beyond that. There are 3 parts of race day
– before the race (pre-race day)
– during the race (race day)
– after the race (post-race)

Before the race
you obviously have prepared with training, most people would be tapering within a week to two weeks of the race. Lowering down intensity and distance, some people maintain short, medium to fast runs.
The 24 hours before some people do carbo loading, that is to eat and drink carbohydrates before the run. I would suggest to do no differently from what you have in the past during training. A common recommendation is to eat a full meal at the least 3 hours before the event, and hydrate youself 1 hour before. What I usually do is the night before i have a fullfilling late supper, and the moment i wake, drink 1-1.5 litre of warm or room temperature water, and the some bites to eat, e.g. Two peanut butter sandwich, a can of tuna, and maybe some fruits (usually bananas). The water drinking may initiate your bowel movement, and cause you to urinate. Do so before going off to the race location. The race organizers may have a warm up session, usually an aerobics session, I rarely join and i just do my own sets of warm ups and stretches.

During the run
During training i may have pushed myself to go further or faster. I am not racing against the elite runners, I am racing to complete the event and do my best. So for the first few kilometers i would really pace myself, sort of warming myself up. Trying not to be to excited by the crowd and speeding up. After that I just maintain my form and focus on that and my pace, a gps watch or smartphone app, or heart rate monitor, can help you maintain your pace. I sometimes admire the crowd filling up the road, and saying hello to the runners i often meet. When there is a supporting crowd, their applause often energizes, but becareful not to get too excited or else you would push yourself harder than necessary. At the the last few kilometers you may gauge yourself and decide whether you can speed it up, or just maintain your pace. Seeing the finishing line often tempts you to go for it though.
On hydration, for long distance runs i try not to rely on organizers and bring my own hydration pack, i take a sip almost every 15 mins, and everytime i feel thirsty. The only problem with this is i rarely bring extra weight during my runs. Some people can run without hydration pack, most elite runners don’t, they take from the water points, but in my my past experience the laggards often suffer from no water left at the waterpoints, therefore i keep myself ready.

After the run
At the end of the run, depending on the organizer, you may receive extra fruits or drinks, a finishers medal and/ or a certificate. Their usually is a prize presentation ceremony that may include entertainment, announcing the top runners, and lucky draw prizes. During this time i would be doing my own stretches, which includes squats for my gluts and hamstring, and lunges for my calf, i may even do arm stretches for my arms and shoulders. You’d be surprised how those would be affected. An ideal event organizer would prepare a meal, but rarely is the case. It is highly recommended for you to rehydrate and op up yourself with carbohydrate and protein within 30 mins of you event. This would also reduce the effect of DOMS, or delay onset muscle soreness syndrome. Basically the muscle pain you feel in the next 48 hours. You would feel the strain you place on different muscles of the body. I highly recommend stretching those parts up. Some people would go for a full body massage instead.
When I get back home or into my hotel room I would usually have my power nap. This usually to compensate for my early wake up for the race.
The next day i would rarely do a workout, give myself a rest, but at times i would like to go for a relax swim, it would give me a work out without straining my muscles. I do see people still running the day after a long run, I have only done that a few times. I would stretch the morning and night for the next 2 days. Then start my training again for the next race.
On hydration, I weigh myself before and after the run, and usually notice. 2kg difference, so i usually try to drink that much to replace the water i have lost.