MultiSlot aka General Modslot Generator (GMSG)

mod slotThis mod allow you to gain new inventory slots with experience levels. By default, you gain 1 slot every 3 levels (can be changed in the conf). You can gain a maximum of 27 inventory slots.Elytra Slot. Adds accessory support to the elytra so you can fly and wear chest armor at the same time. Formerly known as Curious Elytra and Elytra Trinket.