I just polished off the last olives in a jar, and I would love to use the remaining brine somehow. Any ideas?

add some to the leftover pickle juice and brine chicken breasts for frying.

Stir into just-cooked quinoa, instead of vinegar, as suggested here: https://food52.com/blog/7941-how-to-make-quinoa-salad-without-a-recipe
Toss with lots of parsley, including finely chopped stems, which are full of flavor. Add halved cherry tomatoes shortly before serving, along with a handful of pistachios and some feta that you've crumbled lightly with a fork. Enjoy! ;o)

Every time this topic comes up the standard suggestions are:

1. reuse the brine for pickling other veggies
2. use in cocktails (in this case, martinis)
3. use to brine pork, poultry
4. add to soup, stew (paying close attention to saltiness and or tartness)

I probably forgot a few suggestions, I'm sure others will pipe in.