(for those of you that do not know what a Chekhov's gun is see theTV tropes page)
These are the ones I can think of off the top of my head, in no particular order, not counting the ones that were already fired in WoK.
1) the flute Hoid gives to Kaladin, because come on, there's no frigging way that's not coming back! (PS I asked Brandon on twitter and he said Kaladin still has the flute)
2) Those two guys Elohkar was talking to in the prologue, Szeth thinks they weren't important, which just makes me even more sure they are or will be.
3) obviously the black sphere Galivar gives to Szeth, Brandon has refused to answer questions about it and said it's a "major big RAFO" which means it's clearly a major big Chekhov's gun.
4)Baxil's mistress who is almost definitely Shalash.