This is a given and there's more than enough science to back this up, so don't be a helmet, wear one.
2. Water bottle cage and water bottles.
Staying hydrated is essential during exercise and especially during a hot day of road riding where you have no protection from the sun. Keep hydrated, keep healthy and perform better when you're running on fluids.
3. Saddle bag
Taking the bits out of your pocket and handily away, get one big enough for a bike lock, mobile and wallet - everything you need to get around town! You'll notice the difference to those stuffed pocked and won't be able to ride without one again.
4. Track pump with gauge
Just in case the wheels get a bit flat - which they inevitably will. Make sure you wheels are at the right Psi to make the most out of your pedal, which is where a gauge on the pump is really handy.
LEDs are preferable for the high power and low battery usage. Visibility is so important, not just in the evenings, but during a bad weather day also, so make sure to always have your lights onhand.
6. Road shoes and pedals with cleats.
Cleats allow you to use the power from raising your feet as you cycle, which means less energy is exerted and more power is realised. The trick however is to not get caught up when putting your foot down!
A long ride didn't happen unless it was captured! You've all heard the saying 'Pics, or it didn't happen' so make sure to capture everything in an extra wide angle with a gopro.
9. Cycling sunnies
These make a huge difference on the road. They do everything standard sunnies do, but the tighter fit helps keep the wind, bugs and other bits and pieces from nailing you in the eyeball. Being able to keep your eyes wide open also helps you to see more and be more alert.
10. Cycling gloves.
Cycling gloves make you feel more in control of your bike - and definitely help on the cold mornings!