This really isn't everything, it's a start.. in addition:

1. Everyone isn't. If you feel pulling up the pedal would help; look into clip or clipless pedals. If you ride mountain (less common) or cruiser (never?) you've probably never seen.

2. No. If you're willing to accept ribbing/in a Gran Fondo (road) sure. If you're uncomfortable on long rides; look into padded shorts (but note a better seat should be your first choice, and unobvious padded shorts are available). If you're shredding a hill (mountain) then look into padding/protection. If you're on a cruiser and it hurts.. look into a custom fit (#3).

3. There are guides online, there are relatively inexpensive pieces you can buy to improve the fit of your current ride, but if you're uncomfortable/unsure.. it can help. The best money you can spend is on a lock (location dependent) then a saddle (after the bike).

4. Check tyres, oil chain/cassette/pedals. At around 5000Km/5Mm (3000mi) you should check your chain (~$50) - you probably need a new one. If you catch at 50-75% stretch you can save yourself replacing the cassette (~$100) too. With tyres, on a road bike: use a pressure check, on a mountain bike: if you can see a bulge while riding it's low. Oil check: If you can hear the chain/pedals/derailleur they need oil (if you're not sure.. get them fixed up and ride in silence to hear the difference). If you rode in rain last time, all three are probably thirsty (check your shorts if you don't have mudguards).

5. You never need a road bike, unless that's your thing.. but you wouldn't be asking.

6. Wallet and phone. If you're on a road bike, tube failures are common enough a replacement/pump|cartridge/tyre level are helpful, but not necessary (money, phone). If you're on a cruiser or mountain bike you'll rarely see these on a ride, especially if you followed #4, but as a backup: money, phone.

7. No. If your bike route includes sharing the road with cars at dawn/dusk/night - they're useful, and the low end ones (REI, MEC) are only $10/ea (but have to be charged when you need them).

8. Err.. we wear them when it's too warm for full-finger gloves? Gloves, like glasses are basic safety equipment, wear them if you can.

9. Not at all. If you need water for a 1 hour meeting.. then probably. But, the human body is surprisingly good at using water reserves, a 50km/30mi ride in 25c/80f weather is easy. You'll need to consume water when you finish, but no need to worry about it on the ride. If you're going further or it's warmer you should consider it, but don't fret about it.

10. You don't need to, unless you're riding to a restaurant. If you need a snack ever hour, probably. Same as water.. your body adjusts.

11. n/a (don't buy a road bike and accept all the concessions/safety risks if you want to do this)

12. Buy a better saddle, buy padded shorts if you're desperate, get a bike-fit, ride less. It does take you time to adjust, but if it continues, there are parts you can change/improve. Several saddle vendors have measurement devices that help find a good saddle (Specialized in North America).

13. If it doesn't hurt/fly off (why did you buy it if it doesn't fit?). Buckle it (it's useless if you don't). Be aware there's research that shows motor vehicle drivers are worse around riders in helmets (but you may well feel better, plus it keeps the sun off).

14. Ride. Practice. Spin/Stationary bike.

15. You will be yelled at (shake it off), you're likely to be doored (a driver who didn't notice a cyclist coming and opens their door) - give parked cars room, there's a risk of drivers failing to see you (car a-pillars on roundabouts/traffic-circles being an obvious case, also yellow/red light runners) so be aware. Bright colours do bollocks. Red and blue flashing lights are mostly illegal and just annoy other riders. Lights during the day just annoy other riders. Don't break traffic rules. If you like neon... well you're all set, but someone who isn't seeing you, isn't going to be tricked by a dash of colour.