The most common and most likely answer to this crossword clue is the 4 letter word DIBS
D
I
B
S
Buddy explains!

The straight part
We know that "Ready" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ready = dibs.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.
What does DIBS mean?
DIBS noun- The right to use or enjoy something exclusively or before anyone else.
- To claim a temporary right to (something); to reserve.
- Used to claim this right
- A sweet preparation or treacle of grape juice, much used in the East.
- A dibber (gardening tool)
- One of the small bones in the knee joints of sheep uniting the bones above and below the joints.