1. Drink Alcohol - Although alcohol will help you fall asleep faster, it interferes with sleep later into the night. This is probably due to its disastrous effects on testosterone and growth hormone, both of which are released when the body has reached its lowest temperature - usually after 4 hours of uninterrupted sleep.
2. Drink Caffeine - A caffeine blast too late in the day can keep you up. Caffeine takes awhile to clear your system so chill out after 3 p.m. You can take extra Vitamin C to help clear it out and mitigate the effects it will also have on your adrenals. If you are drinking it for the "energy," then you need a nutritional/sleep overhaul ASAP.
3. Spicy and Acidic Foods - Take it easy on the spices before bed. These can cause stomach issues that will keep you up. If you tend to favor acidic foods later in the day (meat being a good example) make sure that you counterbalance your protein with enough green vegetables (broccoli is a great alkaline veggie). I know, I know meat rules - hedge your bet by taking some high quality digestive enzymes with your meal to ensure optimal breakdown and utilization.
4. Workout - A workout to late in the evening will keep you up. Besides breaking a sweat you are promoting the release of tons of chemicals in your body. Some of these promote alertness and can keep you up. If you must train keep it to the strength training side of things - America's obsession with long slow cardio will keep you up and make you fat...how's that for a combo!