Non-usable magic items

The Clever Dice of Invasion is a type of Scoundrel Token, which is a special piece of equipment that the Scoundrel can equip. There are items for the other followers, like relics for the Templar and focuses for the Enchantress. All of these items should be marked "Follower" where the equipment slot is normally listed.

These items can only provide a benefit to your followers and only do so when equipped. If they're sitting in your inventory, then they are just taking up space, and you probably want to equip, sell, or disenchant them.

To equip your follower, you need to access the follower inventory screen. On the PC, you could do this by hitting the F key or clicking on the follower's portrait in the top-left corner of the screen. On the console, you need to access the character menu (the Back button on the Xbox) and navigate to the party screen.