What is the command to select more than one item.

Are you trying to select multiple items on the SUT or in eggPlant?

To select multiple items on the SUT you will simply execute the actions the way the user would. If they need to hold down the shift key and then click on an item further down the list, then you can use the KeyDown command to hold the shift key down while the click is executed, and then release the Shift key afterwards. The code might look like this:

KeyDown ShiftKey
Click "someimage"
KeyUp ShiftKey