property Items.ItemData(Item as HITEM) as Variant

Retrieves or sets the extra data for a specific item.

TypeDescription
Item as HITEM A long expression that indicates the item's handle that has associated some extra data.
Variant A variant value that indicates the item's extra data.

Use CellData property to associate an extra data with a cell. The ItemData and CellData are of Variant type, so you will be able to save here what ever you want: numbers, objects, strings, and so on. The user data is only for user use. The group doesn't use this value.