I reuse them all the time for leftovers.
Recently I started reusing peanut butter jars. They are great to store candy in. I also use them to store leftover hot dogs. They are the perfect length.
I reuse my son's Ovaltine containers, they are great for odds and ends, like buttons or thread, that we don't need access to all the time. I can just put them in the back of a closet and forget about them.
Reused Jif container for jelly beans. I don't have to worry about clipping the bag shut, and it's more cost effective than buying ziplock baggies all the time or storage/mason jars.