They did clarify in the PTR that coffer keys would also be reset with the season for delves.
A random site lists these as the PvE currencies that reset:
Restored Coffer Keys
Undercoins
Valorstones
Gilded Harbinger Crest
Runed Harbinger Crest
Carved Harbinger Crest
Weathered Harbinger Crest
It also mentions to spend undercoins now if you still have any on things like the reagent pouch.
Not sure if season 2 delves have new reagents that they drop? I never looked into season 2 crafting.