I already have my helmet and lights. What other accessories are recommended?
It depends on the weather:
- Rain coat and warm clothing
- Fenders (aka mud-guards)
- Rack and pannier (to carry e.g. any spare clothing, wallet and keys)
- Cycling gloves, and cycling shoes
- Adequate tires (size, width, pressure, thickness, tread, puncture resistance)
- Snack, cell phone, optional first aid for you and/or for the bike, ID, public transit fare
- Tire pump (to keep at home, but to keep your tires at the right pressure; may need to use it at least weekly)
- Lock (a U-lock is difficult to cut, but a cable is very easy to cut)
- Weather report and forecast
- Disc brakes (if it's wet or muddy or hilly, or heavy braking)
You asked about accessories and not the bike; ideally (because a good bike is more fun) your bike is of a kind that's worth servicing, and has been serviced recently: so the wheels spin freely, the brakes work well, the chain is newish, the seat and everything fit you, and the gears if any.
Also, what kind of training should I look at before I go with the full daily commute?
With a good bike and not too much traffic, 10 km is about 35 minutes.
So take your bike out for half an hour or more. Maybe twice in a day. Scout your routes in advance. Enjoy doing it. Feel better for having done it. Do it again.