Student charity event to seize collection (6)
I believe the answer is:
ragbag
'collection' is the definition.
(ragbag is a kind of collection)
'student charity event to seize' is the wordplay.
'student charity event' becomes 'rag' (as in rag week at university).
'to seize' becomes 'bag'.
'rag'+'bag'='RAGBAG'
(Other definitions for ragbag that I've seen before include "Random collection" , "Hodge-podge" , "Odds and ends" , "Motley assortment of things" , "Miscellany" .)