In my most used cabinet I keep several bins and a binder containing pet supplies and information. This has been key to keeping their things contained and organized.
I'm not sure where I got this idea, but several years ago I started a binder of only pet information. All those receipts and print outs and paperwork you get from vet visits. Keep a tabbed section or a plastic sheet protector for each animal and put the most recent on the front. This helps me when I'm wondering when the last time Motley got her vaccines, I can quickly pull it out, open to her tab, and see it was November 6th, 2012. (Time to call the vet and make an appointment!)
Currently we have a dog and a cat. We've previously had another dog and another cat. So over the last five years we've accumulated quite the pet supply collection. I separated dog and cat supplies into different bins. They may like each other in real life, but I do not like when I'm looking for Roux's heartworm pill and come up with cat toys.
Take some time to go through your supplies. Is their old medicine that is past the expiration or usefulness? Do you have medicine for an animal that isn't even alive anymore? Do you have an overabundance of cat toys for a cat who doesn't even play with toys? Weed through the mess. If you have extra, unexpired medicine or toys, consider giving them to your local shelter. They always need these things.