To add several items at once, just hold the control key (Ctrl) while picking the items with the mouse. Ctrl+Click will select the items one by one, each time you click while holding down the Ctrl key.

To select a range of items, use the Shift key. Shift+Clcik for the first one, and then Shift+Click on another item will select the range of items between the items.

Give it a try, and let me know how it goes.

Wa'il