+1 on everything Vireo said.

That being said, I know EVERYONE will have different needs on their bike for rides of 10 - 375 miles. So everyone's list will be different and that's fine. We can all agree to take different approaches to riding and what we believe is essential on the bike.

I have learned a lot about what is and is not essential on every long ride I have done. On my 600k brevet I brought WAY too much food. In fact that's a lesson I still didn't learn at last weekend's double century - I brought WAY too much. After a learning experience ride like that, I take some notes on what did and did not work, what I need next time and what I should leave home.

Here's my list of what is ON my bike for any ride over 60 miles:

2 bottles (2 scoops each SE and power bar endurance)

Garmin

Seat bag: 2 tubes, 3 CO2s plus CO2 filler (what the heck do you call that??), 1 tire lever, 1 multi tool, snack size baggie containing (1) small rolled up piece of duct tape (probably 5" of tape and MAN has that come in handy on brevets) and (2) 3 zip ties.

In the Jersey Pockets: snacks, baggie with cell phone, ID and cash, short finger gloves if it is cold when I start and I think it will warm up.

If the rides get longer and more remote, I start to pack more food, specifically baggies with drink mix in them. On my 600k brevet, I did pack extra shorts and used them happily, but this was the only time I did that. (I also packed and used my rain pants on that ride, more for warmth in the wee hours, though it also did rain).