Fix for latest Rust version.
Facepunch have updated all of the item ID's used in the game, which will break all of the items in the containers. You will see a message in console if the plugin attempts to spawn an item which doesn't exist, with the given ID of the offending box.
To make this easier to fix, I have added a new '/eloot items' command, which will update the items of the box you're looking at, using the items in your main inventory.