Unrestricted. If you are 21 or older, and may otherwise legally possess a firearm, you may have your loaded handgun anywhere in the vehicle, concealed or otherwise. Long guns must be in plain view.
MO recognizes ANY other states CCW permit, which is necessary to CC while on foot. OC is allowed by state law, but may be prohibited locally. Unless you are familiar with the local codes, you should probably avoid OC.