I've been mulling over what I learned or observed during this ride, especially since I'm thinking about a double century soon, possibly from home to Wausau, WI in one shot.
Breakfast. Eat a bigger breakfast. The usual race-day oatmeal prep (steel-cut oats with maple syrup, banana, almonds, etc.) would probably last a lot longer than the spruced-up greek yogurt I had for this ride.
Chews. When I was flagging, the only thing that really picked me up again was Shot Bloks or those gummi fruit slice things. And I found that I was craving those the most. Carry more of this junk.
Regular breaks with stretching. I split the ride into 10-20 mile chunks, which worked fine, but I really need to force myself to stop when I'm planning to stop. And stretching needs to happen at each break, because holy wah was I tight after that ride.
Spare socks, gloves. If it rains, the only wet things that truly bother me are socks and gloves. Easy enough to carry a dry pair of each.
Diversion. There were boring stretches. Sometimes I just can't bring myself to look at nature and think "ooh pretty" or sing along with the same song that's been in my head the entire day. A bluetooth speaker might be worthwhile for listening to a podcast or the news along the way.
GPS. No GPS I own has a battery that lasts longer than 8 hours or so. There will be recharging involved, unfortunately. This means either carrying a battery pack or finding a place to plug in during my breaks.
Boot. I sliced my tire right at the end and had the first flat in recent memory, which would have sucked halfway through the ride. I had paper money for use as an emergency boot, but splurging for an actual tire boot wouldn't be a bad idea.
Chain lube. I used the last of the little sample tubes of chain lube after it stopped raining, so it was definitely worth having along.