If the list has more items that can be displayed, then a scrollbar will appear along the right edge. For a better overview, all selected items are also marked inside the scrollbar. For faster navigation between selected items, right-click on the up- or down-arrows of the scrollbar. The cursor will then jump directly to the next selected item in the list.
If you would like to work with only a subset of the data, then click on the little filter icon to the left of a list item. All the objects that do not belong to this category will then be filtered out (represented as greyed-out, not active anymore) so that you can concentrate on your objects of interest.
