The Iron Chests mod offers a slew of new chest upgrades to maximize space and storage. The iron chest alone can hold as much as a standard double chest.
And from there you can upgrade your chest to gold, diamond, obsidian and crystal. Once you hit diamond level, however, the amount of slots won’t increase. And the Crystal upgrade allows you to see what’s actually in the chest!
You can even upgrade Shulker boxes with all the various colors and upgrade options!