You have to get used to what YOU need on a long ride. I'm guessing it's not for a while, so you've got time to train for both the time and intensity that you'll be riding at in the race. Use your training rides to test food, drink and equipment as well as building pace and stamina. You might find that you prefer 'real' food over gels and energy drink, for example.
I'd agree with a lot of what the guys have said(oddly enough,not the Guinness though )When i was doing 50 odd mile rides,I'd start with a carb heavy dinner the night before(pasta or whatever),breakfast of bacon and eggs,fried slice etc(protein,simple and complex carbs).Once on the go,I'd have Mars bars,peanuts and bananas for snacking,ham and egg rolls for a meal. Hydration was the biggest secret: 2l camel pack,and two 600ml bottle of moonjuice(45%hydrotonic drink,45%isotonic drink,10%red bull). Moonjuice is seriously evil!