The most common and most likely answer to this crossword clue is the 6 plus 7 letter word DOUBLE FEATURE
D
O
U
B
L
E
F
E
A
T
U
R
E
Buddy explains!
The straight part
We know that "Back-to-back films" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case back-to-back films = double feature.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.