Sleep: 7–9 hours daily. If you cannot get that much, take power nap whenever you can. Don't over do with power naps others you will feel grumpy. Limit it to 20 min.
Eat right: Most people get too much sugar in their diet, mainly from refined carbs. This results in blood sugar surges and drops, resulting in cravings and hunger. You need a good amount of protein and healthy fats in each meal. Carb or no carb, no problem.
Drink enough water: Staying hydrated is important. Just a mild dehydration can results in lack of concentration
Do the most important first thing: You see our will power is limited. Ideally you should be done with your most important and creative work before that. I am not sure of your lifestyle, but if say if your college starts at 9am, I am sure you can get in 2 hours of work before hand.
Green tea/Ginger tea/Lemon juice: These are your best friends after water. Drink unlimited cups of these. Just don't add any sort of sugar with it and you are all set.
Coffee is great, only if its limited and sipped before 3pm: Caffeine can certainly give you that boost of energy to get started and keep you alert and focussed for few hours. I rely on it quite a lot to get lot of sh$t done.
Work faster: When you say you want to work for 5 hours or more, think how you can finish the work within 4 or less?
Work fills up the time you usually allocate to it. So work faster.
Work in chunks of few hours: Working in chunks of 90–120 min works best. Your body has a natural rhythm and its best to obey it. You are a super-focused person if you can concentrate on a given task for about 20 minutes or so.
Alternate between standing and sitting:
Take 5 min break every 21 minute: This is simply an extension of the above point. Not only it will save from the detrimental effects of sitting, but you’ll be able to focus way better after taking breaks. Try it and see how it goes.