Basketcase is a mod that adds three different sized baskets coming in small, medium and large. They all vary on the amount of items they can hold but they offer an easy portable storage system to expand your inventory a bit. The small ones have four slots that can hold stacks of four items.
The medium basket is slightly bigger with eight slots holding stacks of eight per slot.
And the large has twelve slots able to hold stacks of twelve per slot.
The baskets can also be set down if you need them out of your inventory and if you hold shift then right-click to pick them up again it’ll retain all your items! These are great for holding extra tools or anything else that may clutter your inventory up and you don’t need access to immediately.