The most common and most likely answer to this crossword clue is the 6 plus 6 letter word RETURN TICKET
I've seen this crossword clue in The Guardian
R
E
T
U
R
N
T
I
C
K
E
T
More clues leading to the result RETURN TICKET
Buddy explains!
The straight part
We know that "something to get one thither and hither" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case something to get one thither and hither = return ticket.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.