The Meaning of Life, the Universe, and Everything.
Chest Cavity lets you use a 'chest opener' to access a secondary inventory. There are some items already in it, but those probably aren't important so you can take them out to make room for other stuff*. It also adds a variety of drops that are similar to the junk you discarded from your extra storage.
Requires Minecraft 1.16.x and Fabric API. Also uses Onyx Studio's Cardinal Components, but that is included in the provided JAR.
*Side effects may include shortness of breath, inhibited healing, inability to fight off infection, vulnerability to physical harm, weakness, loss of nutrition, difficulty walking or running, and sacrifice to Aztec gods .