During the last few long training sessions (20 mile runs) my brother and I have been reviewing race day tactics. Here are some personal tricks of the trade that work for me. Everyone is different, so find what works for you. Maybe some of these ideas will help you.
Starting a week or so before your big event, spend a day or two eating primarily protein. You want those muscles strong and happy. The remainder of the week should be spent "carb loading.". Carb loading does NOT mean overloading, though! Eat your normal quantity, maybe a tiny bit more, but not more than your body can handle. No amount of overeating will make you race better.
That said, there is the delicate issue of the infamous "runner's trots." This may be a non- issue when cycling, but some people do experience digestive problems during any kind of heavy exercise. At the risk of a little ickiness, I'll share the solution that works for my body. If my race (or long training session) is on a Saturday, I will take a mild, natural laxative (senna) on a Tuesday night or Wednesday morning. Clearing out the digestive track mid-week, then being careful not to over-eat the rest of the week, makes for a lighter and more comfy race. Do NOT try this - or any unusual tips - for the first time at a race. Try the tips on long training sessions and find out what works for you.
More on this delightful subject (for many it is a very frustrating problem): avoid high fiber foods the day before the race. Choose foods that are easy to digest. White rice, pasta, light breads, for example.
Many races offer a big carb dinner the night before the race. Pasta is the norm, although here in my Idaho town a potato bar is the pre-race dinner for at least one race. Other races off a wide array of breakfast foods right before a morning race. Fearing the big bonk, people pile up the food and dig in. Unless you have a stomach of steel, I would recommend restraint. Go ahead and eat a little, but realize you are not going to starve on a 3-4 hour or more race. You can fuel along the way. No need to pile it up and have it sitting in your stomach - undigested, unusable, and uncomfortable - like a rock. Instead, eat your biggish (not huge!) meal at lunch the day before a morning race.
As for hydrating don't go overboard on that, either. Your body can absorb only so much liquid, and unless you enjoy frequent port-a-potty visits, drink only what you need for the time being. Like fueling, you will be able to hydrate along the course. Be careful not to under-hydrate - my approach is to at least drink to thirst, then a little more, and also to drink every time I fuel or at least every half hour. It's always best to drink before thirst kicks in. No need to chug a quart of water, a few swallows or even a cup or two might be enough. Again, pay attention to your body on long training sessions to figure out what works for you.
Energy gels are the bad guy for some people. In an effort to keep energy up, people gulp down an energy gel, then wonder why they feel worse than ever. They experience stomach cramps or feel heavy, or like they have a weight in the pit of their stomach. The very thing intended to keep them going is slowing them down. This has happened to me enough that I either had to give up fueling with gels or find a solution. I found a solution. Instead of chugging the gel, try squeezing a little out at a time into the pocket of your cheek or under your tongue. Doing it that way helps you not taste the horrid, sometimes sickening taste of the super-sweet pseudo fruit/chocolate/whatever flavor. Let it dissolve slowly, sip a little water or sports drink if you can, then when you're ready do it again. It can take a good 5 - 10 minutes this way, but for me it's the only way I can tolerate the stuff. I can feel when fatigue is setting in, and after the gel I can feel my energy levels jump up. My brother laughs at me on our long runs as my talking dwindles to nothing, sinking along with my energy. When the fuel kicks I start running with a bounce (he says) and I feel like a little chipmunk chattering and chatting away. I am sure it annoys him, but he's a good sport.
Ladies only: if Aunt Flo is prone to unexpected visits, especially when you are putting extra stress on your body, prepare accordingly. A small, sports specific tampon could save your race.
Another thing that has helped me tremendously was a bit of advice from my brother. I have no idea if he made it up or if it's an old wives' tale, or if it is actually true. I do know that it has helped me and so I want to (and do) believe in this idea. He said we run off the sleep we had two nights before, not the night before. Why is this such a big deal? Well, many racers simply do not sleep the night before a big race. Nerves kick in. Nervous about the race, nervous you have forgotten something, nervous you'll oversleep, you name it - you'll likely be nervous about it, particularly if racing is new to you. I actually get those same reactions the night before a long training session.
So the mental battle begins the morning of the race. You are worried you won't race well because you didn't sleep well, or you didn't sleep well so don't even try to do your long training session. But armed with the advice from my brother, you are now empowered to race anyway and to know you'll be just fine because two nights ago you had a good night's sleep. Behind a good race is a lot of good thoughts. If you think you can, you're probably right. If you think you can't, you're probably right then, too. I found, anecdotally, that this bit of wisdom held true with newborns and sick children that kept me up all night. I could function just fine the first day (going off the sleep from two nights ago?), and crash the second day.
Just a tidbit here, if chafing is a problem, it's best to deal with that before the race than have to hurt in the race itself. Long training sessions will help you figure out where then rub is, if any. I put Vaseline between my toes and under my arms because those spots are an issue for me. Take bandaids in your pocket if you expect a rub that'll need some extra protection. Men often chafe and bleed on their chest so bandaging up beforehand is a good idea.
Next, Ibuprofen. Don't take ibuprofen (Advil) or other medications that will mask the pain of an injury during a training session. You need to feel the injury so you can respond appropriately. During a race, however, it is kind of too late and if I intend to compete despite a potential or existing injury, then I take my Ibuprofen before I race so it doesn't hinder me. I am not suggesting anyone else do this, just saying what I do. Athletes do not always make the best decisions when competing is involved.
Self-talk can help in all stages of a race. Walk yourself mentally through the race. Do you have all the items you need? Make a checklist on paper so you stop fretting. Imagine yourself speeding along, a good cadence, a nice stride, a long stroke. You are in the groove. You feel the high and you can go forever. During the race, pick landmarks to reach, find people to pass or pace, talk positively to yourself - or yell at yourself if that's what keeps you going. Again, a good part of racing is the mental battle waged between you and yourself. And just keep going. You won't finish any sooner if you stop.
After then race, take some Ibuprofen if you haven't already. Stretch out, walk around, ice up. To help avoid sore legs, I pull on the compression socks I bought to combat varicose veins during pregnancies. I will even sleep with them if I have had a particularly hard or hilly race or training session.
These are just some ideas, like I said, that work for me and may work for you. Again, don't try anything drastically new during the race. Figure it out during long trainings rides or runs to find out what your needs are and how to best address them. Happy trails.