+1 to all above, especially Muirenn's comment about shifting and stopping/starting.

What kind of bike do I need and what are the trade-offs if you cycle in varying conditions (I'm still asking that one)

Emergency braking technique

How to get on and off bike

Proper locking technique and what are the weight/effectiveness trade-offs in locks

How to carry stuff on bike

What to eat and drink before/during/after a ride

Which accessories do I really need, and which are nice but optional

How to adjust saddle (lots of people don't realize how easy and important this is)