I work at an Eastern European restaurant so naturally we have a lot of pickle brine remaining.
If the brine is any good, you can use it to “repickle” something - we heat it back up and pour over new vegetables. This works if the brine is particularly strong.
You can use it to add acidity to soups and salads like you might with vinegar. I’ve also heard you can marinate meat with it, though I’ve never tried it.
You can also start enjoying pickle backs or martinis with pickle brine.