Small box for valuables (6)
I believe the answer is:
casket
'small box for valuables' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for casket that I've seen before include "Jewel-box" , "Box for jewellery, or corpse" , "Small box for holding jewellery" , "Small box or chest" , "Helping boost" .)