Pace yourself. Are you pushing hard to complete all your longer rides at the same speed? If so, don't. Technically, you don't need to eat anything to complete the ride. I've ridden 40 to 50 miles plenty of times without eating anything before or during the ride, it's simply a matter of energy management by pacing correctly.

If you are riding hard, nutrition and hydration can help, but it cannot overcome a critical error in pacing. Food and drink are not magical.

Good luck and enjoy it. If you've ridden 35 miles, 50 miles will be within your reach. Happy birthday!