In the Types list you see the list of resource types of the selected resource file. You cannot select more than one item in the Types list, but you can select items in the IDs list. If you keep «Cmd» (apple) or «Shift» modifers while you select items in the IDs list you will get different kinds of multiple selections. You may not select already compressed items whose name begins with a ◊ (diamond). For the program it means it is already compressed. For your convinience you can select everything in the IDs list by selecting an item in the Types list and keeping the «Cmd» (apple) key, and delesect evrything in the IDs list by keeping the «Option» key.