Your objectives are quite reasonable and the only real difference with the longer ride is needing more calories along the way. I have always found raisins to be easy to eat while riding, easy to digest, and they provide a lot of calories for energy. I start with a high carb breakfast of pancakes which are easy to digest and do not slow me down out on the road. I avoid eating meat which tends to bog my body down.
I would focus on maintaining a constant speed but do not worry if a head or side wind makes it more difficult and you need to slow down. Having other riders to block the wind will allow you to use a higher gear and lower RPM's. But be very careful as if your front wheel hits the rear wheel of another rider you are likely to crash and find yourself on the ground.