Satisfied with what’s inside (7)
I believe the answer is:
content
I believe this clue is a double definition.
'satisfied' is the first definition.
(similar in meaning)
'what's inside' is the second definition.
(the contents of something)
'with' acts as a link.
(Other definitions for content that I've seen before include "substance of book?" , "Gratify" , "Elements" , "Satisfied; volume" , "Quietly happy" .)