Idiots take in tip-top possessions (6)
I believe the answer is:
assets
'possessions' is the definition.
(asset is a kind of possession)
'idiots take in tip-top' is the wordplay.
'idiots' becomes 'asses' (I've seen this before).
'take in' indicates putting letters inside.
'tip-top' becomes 't' (top of the word 'tip-').
'asses' going around 't' is 'ASSETS'.
(Other definitions for assets that I've seen before include "Total value of possessions" , "One's total goods" , "Valuables, things worth having" , "worldly goods" , "Valuable property" .)