Here's a cool DIY idea for a cat enrichment toy. Glue together a group of toilet paper rolls inside a tissue box and randomly fill the tubes with treats. Your cat will be stimulated when they "hunt" for a treat. So simple and inexpensive.
Use Ikea Knuff magazine files as under sink storage holders. Screw a magazine file holder to the inside of kitchen cupboards. Add space to store more bulky items like chopping boards, cleaning products etc.
In the bathroom: Trones boxes fit into tight corners to provide a little extra storage. These little guys can go pretty much anywhere. How To Use IKEA Trones Storage Boxes in Every Room of the House — From the Archives: Greatest Hits