How long can you store olives in the fridge?

That depends on the packaging. If you bought a jar of olives, you can keep them for quite a while - a year or so (check for a date on the lid). If you opened a can of black olives, and are storing the leftovers, I wouldn't keep them more than a week or two, and only if they're stored in a sealed container with the liquid from the can. The same is true if you bought olives from the deli - not pre-packaged in jars, but scooped from an open container.

Usually a year or longer. Look for the date on the package.