I read that diet soft drinks can actually make you gain weight because they confuse your body with the seudosweetener or whatever crap they put in it. As for coffee, moderation is a good idea. Drinking 6 cups a day isn't going to help you out. For one all the caffeine is going to fry your circuits. Coffee is a diuretic so you’re going to pee all your water out (that’s a bad thing) and get kidney stones. Kidney stones are excruciatingly painful and are considered more painful than childbirth.
Bottom line, drink lots of water and avoid pop/soda like the plague. As for food ideas, Quaker instant oatmeal would be a good idea. It will fill you up, and give you energy for a longer period of time. Fruits are excellent because they have tons of fiber and are mighty tasty.
Avoid deli meats because they are full of salts and other crap. Chicken and whole wheat breads are your best friends. Don’t forget veggies.
Oh yeah EXCERSISE REGULARLY! Exercise helps you get rid of stress and produce chemicals (I can’t remember which ones) that make you happy. Plus you’ll look better and make more money.