Can't fit all your tools in your hotbar? Store your hotbar in a bundle!
It has a vanilla-friendly way to upgrade a bundle to become a hotbar-swapping machine. Simply enchant a bundle with "Toolbag" to upgrade the bundle. Then you can store your inventory by clicking Shift. You can retrieve your items with Right Click. And if there are any items already in your hotbar, it will swap them between the hotbar and the bundle.
Multiplayer friendly, balanced for vanilla (more storage on you also means greater risk if you die), and intuitive to use!