If you very recently purchased the gold upgrade and the items are missing from your in-game inventory it probably means the game needs to be restarted. The gold items work differently because they pre-date the regular purchasable items and are actually sold as downloadable content (DLC). While the game is launching Steam checks for any DLC-related items and adds them to your inventory.
The same applies to gold benefits like character slots and customization: the game needs to be restarted because Unturned only checks for DLC ownership during startup.
If you are missing items from the Stockpile (item store) please refer to this article instead: Missing recently purchased items