F&S means Field and Staff.

It might be helpful to locate a brigade inspection report (usually a twelve-page form), which enumerates all members of the brigade, present and absent, including brigade staff.

A brigadier general was entitled to an assistant adjutant general with the rank of captain, an assistant inspector general with the rank of captain, a quartermaster with the rank of major, a commissary with the rank of major, an ordnance officer with the rank of 1st Lieutenant, an aide-de-camp with the rank of 1st Lieutenant.

There was also a senior medical officer, customarily the ranking surgeon from the brigade. If commissioned staff officers were absent, the brigade commander could appoint company officers or regimental staff to act in their places. It was also possible to have volunteer aides, non-commissioned officers and enlisted men acting with the brigade staff, but non-coms, enlisted men and volunteers are never included with brigade staff at inspection.

For what it's worth,
'Bde' is a twentieth-century military abbreviation not used at the time of the Civil War.