Oftentimes, cabinets provide too much headroom for what actually goes in them. In order to take advantage of this extra space, you simply need to add some more shelving.
Vertical dividers in kitchen cabinets are great for neatly organizing cookie sheets and pot lids. You can attach wire organizers to the inside of the cabinet doors to store small packaged items like garbage bags and plastic sandwich bags. And make sure that all clothing rods in closets have shelves above them for extra shoebox storage.