Funny - I've been thinking about this very subject as I need to do 5 hours on-type 'training' with an instructor for the syndicate I've joined. I want to get the most out of it so have been thinking about what's missing from my 'flying toolkit'.
So far my list consists of...
Spins/awareness - have only spun once (I know this is contentious..., let's not start another thread on this)
Never transitted proper controlled airspace.
Never filed a flight plan.
Cross-channel procedures.
Leaning.
That should take 5 hours - what with landing the thing as well!
p.s. No comments about my excellent (alcohol-induced)
leaning abilities please