Congrats on the first ride.
I'll second what CraigB said, it's like jumping out of a plane. The first one ain't that bad. The second trip out the door is scary as all but then after the 5th jump (ride) it's all good.
What's in my seatbag?
- CO2 cylinders and adapter
- patch kit
- tire lever
- spare tube
- the box top from the spare tube (this is for the hole that you might get in the tyre that needs to be covered so you can limp home)
- a $10 bill so I can stop and get Ice Cream and Chocolate milk
- a pump is mounted to the frame. I use that to make sure the tube is partially inflated and the bead is good on the rim before using the CO2
Advice:
- Make sure the bike fits you.
- NO(!) soft seat
- Padded Bibs
- wicking base layer if not just the top (UnderArmor type stuff)
- learn how to remove a tyre and patch a tube when you are at the house. When you are on the side of the road in 90 degree heat with the sun blazing down on you is not the time to learn.
- Tyre lever(s) are for taking OFF the tyre not installing them. Too many pinched/new hole in it tubes that way.
- When (not IF) you get a flat on the road make sure you know what made it go flat by inspecting the tyre real well. I have marked my tyre with a sharpie on the drive (right) side at the valve stem. That way I can know about where the hole is in the tyre with respect to the hole in the tube.
Last but not least... ride it like you stole it.