Jerry,
The 18th Ga. was formerly designated as the 1st Regiment Infantry,4th Brigade Georgia Volunteers(at Camp McDonald); they were issued the U.S. Model-1842 smoothbore musket.

The 1st & 2nd regiments were designated as "Heavy Infantry". They were issued the standard gray uniform issued to Georgia State Troops(Gray kepi,pants w/black stripe); One book states "frock coats" but photos(of soldiers of the 4th Brigade) taken at Camp McDonald clearly show shell jackets.
At the time the soldiers arrived at Camp McDonald (June-July 1861) they would have had various non-regulation uniforms that they were provided to their companies; then they would have been issued the standard state uniform shortly thereafter arriving at the camp.