ok so i have been condemning that snowspeeder luke for a while now but maybe it DOES exist.
when we first see pilot luke in esb hes wearing his flight suit but no helmet and certainly no skull cap (as he is leaving and 21b says "take care sir"
the whole time he is talking to han up till he enters the speeder with dack and puts on his helmet he isnt wearing it.
the last time i was watching empire i noticed that in several shots the best of which is when luke looks up at the approaching walker right before he grabs the harpoon gun
and when he looks up at the exploding walker he does indeed seem to be wearing a skullcap underneath!
once he arrives on dagobah though again no skullcap. im thnking that either he put it on with the helmet like it was stuck inside already
or he took it off during the long trip to dagobah but that wouldnt explain why he didnt have it on already before the battle.
im going with the already in the helmet theory.
let me know what you think