Explain how to RBF (replace by fee) and when they should use it.
I think that CPFP should also be in the list.
And, as some have also mentioned, cold storage is a must. And it can be done easily with an USB stick and a Tails OS, no need to anything more fancy.
Adding extra words after a seed could be also interesting. Maybe also multi-sig.
And back to things I didn't see suggested: the derivation paths may worth a close look too.
Also people learning how to use a block explorer - for fees, for checking whether a tx has unconfirmed parents and how far, maybe other things too - is a must.
Dust amounts, transaction size and its cost based on size, or coin control are also useful topics.
