Air: Stunt plane, mini jet, biplane, bomber, (If ish space, MAS Fighter), Blackhawk
Ground: Maybe LCVP for water, Humvee, M-35 transport, Longhorn (Fun off road vehicle)
Defences: AA gun, Heavy Machine gun. You should also get the battle ship and that Stryker thing that stratofortress made, so we can use the turrets from them.
These are just the vehicles that are used in a lot of modern war things, and that are a lot of fun. (Im not saying you should get all of them.)