Minecraft wiki entry for Storage_minecarts, associated text: Through the use of minecart cramming, infinite storage is possible. If you build one using the schematic on the right, don't forget to put a rail on top of the lower hopper so you can place as many hopper minecarts as you like on it to expand storage capacity. For the minecarts not to spill, it is important to place blocks to both ends of the rail. Be careful to only put items of a single type in the upper chest, you will only be able to access items flowing out of the minecarts into the lower box. As they only flow one by one, different items will only flow out after all of the "same" items are out.