The Blueprint Update lets you archive items that you do not want to see in your inventory. These items are added to the Archive tab.
The Archive is a tab in the Manage Inventory and Player Trading screens. Players can hide items they don’t want to see. When an item is archived, it will only show on the Archive tab. Archived items will no longer show in Manage Inventory, Garage, or Player Trading tabs.
You can search for items that are archived by selecting the Archived option from the Filters drop-down. This filter has been added to the Manage Inventory, Player Trading, and Garage tabs. Archived items can also be Favorited.
Items marked to Archive will show on your current tab until you move to a new tab. When you come back, the archived items will no longer show. At that point, those items will only show on the Archive tab.
You can remove an item from the Archive tab by clicking the Unarchive button.
For more info please check out, How do I Archive my items in Rocket League?