Cases crack in toboggan (7)
I believe the answer is:
luggage
'cases' is the definition.
(I've seen this before)
'crack in toboggan' is the wordplay.
'crack' becomes 'gag' (I've seen this in other clues).
'in' is an insertion indicator.
'toboggan' becomes 'luge' ('luge' can be a synonym of 'toboggan').
'gag' put into 'luge' is 'LUGGAGE'.
(Other definitions for luggage that I've seen before include "Traps" , "(Traveller's) suitcases" , "Trunks and cases of traveller" , "Cases etc for travel" , "Traveller's bags etc" .)