probably the basic stuff would be most useful. you have a doom techbase style going on here, so i'd say just rocky cliff and ground for outdoor areas between bases would be nice. it all kinda depends on what direction you are going in with this pack? continue the techbase theme? expand to other themes/levels, like urban, hell, scifi spacestation, outdoors areas like desert, mountain, forest
also thanks for cc0. it is the most useful license.