Are there any Ghost of Tsushima Missable Items?

Ghost of Tsushima has no missable items. You can still collect any items you don't have after reaching the ending of the game. 

There are no missable quests as well for either Main Tales, Side Tales, and Mythical Tales.

The most important items in the game are also non-missable, the game provide them to you just by following the Main Tales, which are the main quests of the game.

Visit our Ghost of Tsushima 100% Walkthrough to get more details.