On any given ride I'll try to take the least amount of stuff in my jersey/jacket pockets. Above are my go-to items. On longer mountain bike rides, especially if it's hot, I'll bring along my CamelBak Lobo, and pack it full of food and the all important 8-hour bug spray. The Northeast has some of the worst bogs and consequently the biggest mosquitos I've ever seen. See what I bring after the break.
Topeak Race Rocket It's super compact, with an extendable hose, which makes pumping a lot easier. It's Presta and Schrader valve compatible. It also goes up to high pressure in no time at all. Great design.
Park Multi Tool Has just about everything you'd need for minor to reasonably major repairs. It features a chain tool, tire lever, spoke and hex wrenches. I'm only complaint is that the 8mm hex bit falls off from time to time.
Park Super Patch No glue, or waiting, and reliable most of the time.
Rapha Essentials Case Good for keeping wallet items dry including my iPhone.
Bicycle Permit It costs $5 for life, and allows you to bring your bike aboard Metro North and Long Island Rail Road.
Cash Even $1 can save you on any given ride. I can usually buy either a Snickers bar or 3 bananas.
iPod Shuffle Good for training rides around the park. I normally don't listen to music on long rides. I think it's dangerous. The park is fine since there are fewer distractions to be mindful of.