Stuff to study intensively (4)
I believe the answer is:
cram
This clue is a double definition.
'stuff' is the first definition.
(I know that cram is a more specific form of stuff)
'study intensively' is the second definition.
(I've seen this in another clue)
'to' is the link.
(Other definitions for cram that I've seen before include "prepare for exam" , "jam" , "Feed greedily" , "Study hard for exam" , "Study intensively" .)