Yes, pack some good nutrition in now. By good nutrition, I mean food that is high in micronutrients and low in calories. Drop addictive stuff like caffeine now to prevent headaches. Avoid sugar, fat, salt, dairy, processed food, poor quality (feedlot) meat and oil. Go checkout http://www.vegsource.com
http://www.ravediet.com
http://www.processedpeople.com

Do that and you will start your detox early

Mouseclick was right on target. It is very important to wean off "addictive" foods like caffeine, Sugar and chocolate and anything you tend to crave on a regular basis. The discipline it takes to not eat the foods you love and crave will make the discipline of fasting much easier.

One thing I would suggest is to get a good quality green powder ofter referred to as a "Super-food". Take one or two servings a day. These green foods made from dark green veggies and often sea vegetables too will supply you with vital minerals the body needs. Also drink a glass of hot water with the juice of a lemon in it every morning to help cleanse the liver and stimulate the colon. Try and avoid medicines, even laxatives right now so you will not have to deal with that aspect of detox.

Good Luck