I have tons of buttons. My mother had a button jar and I was fascinated by it when I was a child. Since then I've inherited some, and collected a lot more. Fortunately, I use a lot of embellishments in my quilts so they don't go to waste.
I have my medium and large sized buttons in Mason jars, sorted by color. I love how they look on the counter in my studio, they're so cheerful and remind me of my childhood.
I use a lot of small and mini buttons and those I store in Darice bead plastic boxes. These are pretty large with a lot of rounded bottomed sections. I sort by color and style, (printed, polka dots, etc.). I also make my own buttons and store them in the same containers. When I start working on a project one of the first things I do is go through all of my embellishments and make a kit of everything I think I might use. For this I use small plastic storage boxes I get at the dollar store. They're great for putting together a travel kit as well.