If you find your little case of the Monday blahs extending well throughout the day, and the week, you might want to look into foods and eating habits that boost your energy and prevent you from falling asleep in the cubicle.
First of all, jump-starting the day with breakfast is a must: high-fiber cereals with milk or an English muffin with peanut butter are deal, as complex carbs paired with protein make for more energy throughout the day.
Also, since the three meal per day plan can create spikes and lows in your energy, due to fluctuating insulin levels, eating a smaller meal every three to four hours helps keep the amount of insulin you release at a minimum, allowing you to maintain your energy level.
In addition, be sure to opt for snacks with plenty of fiber and protein, like trail mix or nuts. And as far as caffeine goes, if you can't give it up altogether, one cup of coffee is enough for a little boost. Oh yeah, and stay away from those zero-calorie foods - if it doesn't have calories, it certainly won't feed your body.