At home, for permanent storage, I use both Stepped Foam, and Plano compartment boxes. But on the water (OK, y'all can laugh at me all you want, but it works.....), nothing works better for me than Altoids boxes. I use silicon to make a water-tight gasket around the lid, and glue foam to the inside to hold flies, and I glue pieces of float-foam around the outside edges, below the lid, so it will float if dropped. Then, I paint the outside bright orange or red, so I can find it if I drop it. The foam is leftover from when I buy stuff that comes packed in it. I never throw stuff away that can be re-used. I've also used leftover Styrofoam.

I grew up sort of poor, so I learned to use what you can. It's a habit I can't seem to break, even after 50+ years (and drives my wife crazy....).