The most common and most likely answer to this crossword clue is the 16 letter word KNICK-KNACKATORY
K
N
I
C
K
-
K
N
A
C
K
A
T
O
R
Y
Buddy explains!
The straight part
We know that "trinket collection" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case trinket collection = knick-knackatory.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.