Yeah but easier, all you need to do is export the backpack used in the demo into 3Ds max then import yours, and weight it to the same bone which should be spine 3 and remove the demo backpack and export and import it into unreal, You only need to export it with the skeleton from max and when you import do it twice just change the naming and un-click the import skeleton option, that way you get the skeleton and static mesh to setup your new item, make sure you select the Mannequin skeleton when importing your new items.
Like Rhynedahll said the static mesh is used when you create a actor for dropped items and its also used to create a icon.