As favours, prepared to keep in store, packaged (8)
I believe the answer is:
Here is my best explanation:
'as favours prepared to keep in store packaged' is the definition.
I can't judge whether this defines the answer.
'prepared to keep in store packaged' is the wordplay.
I cannot quite see how this works, but
'prepared' could be 'set' (I've seen this before) and 'set' is found within the answer.
an anagram of 'store' is 'rotes' which is located in the remaining letters.
No letters remain.
This may be the basis of clue (or it may be nonsense).
(Other definitions for rosettes that I've seen before include "Badges in the form of flowers", "Leaves", "Set store by ornaments made of ribbon", "Eventing awards", "Set store on floral badges", "Favours, prize badges", "Floral-like ornaments made of ribbons" and "Circular ribbon badges".)