For my DSLR, I have a translucent 35mm film canister from some Fuji Velvia that I cut out to fit over my pop up flash. It's tiny, and it does a nice job as a diffuser. It wasn't my idea. It's all over the internet. But it works, it was free, and it's small enough to fit in my camera bag and forget I even have unless I need it. I also have a second one with a small strip of white paper glued on the front directly in front of the flash to diffuse even more light and bounce more of the light around. And I have larger ones made out of translucent plastic bottles for my speedlights. I store them in my camera bag with a lens inside them so they don't take up any additional room and serve as an extra layer of protection for my lenses (though not really necessary).