Unless this is a mountainous century ride, the biggest difference between 35 miles and 100 miles is eating and drinking. You can probably do a 35 mile ride without eating or drinking anything during the ride. On a 100 mile ride, you are going to need to refuel. A supported century ride will have rest stops every 20 miles or so. Try to drink at least one full water bottle before the next rest stop, possibly 2 bottles if it is a hot day (or you are a large person). Also pick up some food at each stop and eat it while riding to the next stop. Eat and drink what you are used to; you don't want to get a stomach ache or allergic reaction half way into your ride.