Missouri
Make sure you have a CCW that Missouri honors if you intend to carry it, OK for non resident to have in car without it if over 18.
Check your state on here:
http://www.handgunlaw.us/
Read about where you cannot carry on here:
http://www.moga.mo.gov/statutes/C500-599/5710000107.HTM
Add buses and the St. Louis Metrolink light rail system to the list.
For posted private property not specifically listed, carrying constitutes trespass with little consequence the first time, but don't risk repeated offenses.
No requirement to retreat from your occupied domicile or automobile. Domicile includes tents, RVs, hotel rooms.
Do not exhibit weapon in a threatening manner unless necessitated as part of lawful act of self defense.
Deadly force not permissible to protect property.
Lawful to protect third person.
No requirement to inform during traffic stops.
No open carry in many counties--no listing is available.
Don't cross into Illinois with a handgun unless passing all the way through without staying over, and then store as prescribed in Federal law.
Do not take this as legal advice.