Images: Sherwood Forlee
Another "why didn't I think of that moment" comes from this fantastic double-ended jar design by Sherwood Forlee.  Called the Easy PB&J Jar, the jar is designed to help you access the residue left at the bottom without resorting to cracking it open.  As the jar empties, you simply flip it over ad unscrew the other end. 

The Easy PB&J Jar is still a prototype. Have a look at the work done by the designer here.