Well I did a 30 mile look last week and it nearly killed me, this week I made some changes and it went much smoother.
#1 I brought 2 bottles this time, one was a frozen bottle of thinly-mixed Gatorade that at the 2 hour mark was nice and cold. My energy level after the 2 hour mark was greatly improved and so I didn't slow to a snails pace after that.
#2 I have a mountain bike with straight bars, on hills and other areas I find I am putting a lot of pressure on my hands leading to numbness. I am moving my hands closer to the center of the bars during this time, the numbness is reduced and I find that I can push a bit harder and the wind isn't pushing on me as much.
#3 I took a small break to investigate one of the small cemeteries I pass along my route. I felt a bit guilty about intruding on the grounds, but it is a historic landmark. So I wandered around taking shots with my old iPhone. The gravestones were very old for the most part...