Offhand Anything by xAssassin
Supported versions of minecraft

This pack allows you to swap your mainhand and offhand slot items, giving you an extra inventory slot and allowing you to use its slightly buggy features.Due to some limitations, you aren't able to use rockets to boost elytra when in offhand, you cant eat items while they are in your offhand and you can't place blocks while they are in your offhand. Your mainhand still can do these features.