Gonna have to mostly agree with Dave Cutter but his listr is more inclusive than mine...

1 tube
1 patch kit just in case
1 tire lever (which I usually don't need)
1 CO2 inflator, threaded
2 or 3 CO2 canisters (16 g will nicely fill a road tire)
tire boot (park boots are cheap, and they stick so they're easier to use than a dollar bill)

For LONG rides away from civilization, I'll add a multi tool and an extra tube. I do have one of those tiny pumps (lezyne road drive) but DAMN they're a PITB.

Always carry a cell phone, credit card, ID and the uber app just in case.