Brackets that mount under the shelves to the back wall.

Or simply install dividers---like a bookcase.

Shelf standards and brackets work pretty well.
Knape & Vogt is one large maker.

It sounds like you don't want vertical panels breaking up your shelving spans but adding them would allow you to move the shelves up and down as desired. They will also prevent bowing. You will have to add a lot of undershelf supports without them, which starts taking away from your clean look. We purchased our pantry from Closets Central. They have machined melamine that you install yourself and you save a ton buying direct.

Here is a link that might be useful: Closets Central