I also think in terms of time, not miles. I always ride roads to "nowhere", thus no place to stop and refuel, so I must bring everything I'll need.
This last weekend I did my longest ride (80 miles) and brought lots of snacks. In this heat, hydration is my number one priority. I had my Camelbak, and 3 bottles of fluid (2 cages and my aero bottle). For food I brought Paydays, fig newtons, beef jerky, sport beans, and GU. I always bring far more than I'll need to eat and a variety of things, because I never know what's going to taste good 3 hours into a ride.

Have fun out there. I would surely bring some light snacks on your ride this weekend. Have a great time, and let us know how it went when it's over.