This topic can be broken down into 2 separate categories.
Days prior to competition:
This was the first real focus of study that lead to the "glycogen loading" concept. Without going into a lot of scientific history, the typical routine now is to gradually reduce training volume and intensity while increasing the fraction of the total diet that is carbohydrates. This will help the muscles load up extra glycogen (the main fuel for muscles) for the game.
In soccer, this is not a common practice unfortunately. Most research shows that the muscle glycogen levels of (male) soccer players are no better than the spectators in the stands - not good.
Studies on soccer players have shown that those with the most pre-game muscle glycogen run the farthest at the fastest speeds during a game. As such, it is surprising to see that glycogen loading schemes have not been as universally adopted in soccer as they have in traditional endurance sports like running, cycling, cross-country skiing and triathlons.
Five to six grams of carbohydrate per kilogram of body weight over a 24 hours period is the typical suggestion so read those labels on food packaging. Remember, 1 pound of body weight/2.2 = kilograms of body weight.
Day of Competition:
There is probably no more area full of misleading information than eating the day of competition - the proverbial pre-game meal. Most pre-game meals are eaten in the 3-4 hours prior to competition. But realize that the food eaten will have little to do with the energy expended in the game. That comes from what was eaten in the 2-3 days prior to the game.
Most players eat what they like so they won?t still feel full come game time. Remember that the more calories (i.e. fat and protein) in a meal, the slower the food leaves the stomach. Carbohydrates are always the best choice as fruits, cereals, juices, pancakes/waffles etc. over sausage, eggs, steak, or many choices on the breakfast menu at a fast food restaurant.
Food in general, and carbohydrates in particular, should be avoided in the last hour before play. Carbohydrates stimulate an insulin response which lowers blood sugar and also stimulates the production of serotonin, a chemical in the brain that reduces arousal (makes you listless and sleepy).
Both are obviously counterproductive to competition. If something must be eaten, choose low glycemic index foods as they cause less of an insulin response.
Immediately prior to competition (in the minutes before kickoff), carbohydrates can be taken in. The excitement of the game will counteract the insulin response and the fresh carbohydrates give the muscles an extra source of fuel. The type of carbohydrates is important. Foods should be of a moderate or high glycemic index (see table).
Carbohydrate supplement drinks work great. "Clear" candies (jelly beans, "Gummy" candy, Skittles etc. you get the idea) are another choice. .
“Eating to Play.” US Youth Soccer, www.usyouthsoccer.org/news/eating_to_play/. Accessed 5 Apr. 2019