Overcoats and other superfluous items not needed for an approaching summer campaign season were typically turned over to the Quartermaster Department to be stored:
(Civil War Letters of Hezron G. Day, C/16th Vermont) June 16 [1863], we have just packed up our overcoats in a box to send to Alexandria to stay until we come home. We do not need them now and we do not want to lug them in case we have to march anywhere. This makes our knapsacks quite light.
(Frederick Watkins, 4th New York Battery) June 6 [1863], camp near Falmouth, Va – we have been ordered to turn all our surplus baggage over to the Quartermaster, knapsacks and all unless we choose to keep those knapsacks, but if we do, we shall have to carry on our backs. Gen. Hooker has issued an order in which he cuts down every man’s allowance of clothing: ... cannoneers allowed one blanket and the drivers one overcoat. The cannoneers are not allowed any overcoats, nor the drivers any blankets. The drivers being expected to use their horse-blankets and overcoat to sleep in.
(Voices from Company D, 5th Alabama) March 30, 1863, extra baggage in the army sent to Richmond for storage [beginning of the campaign season].
Officers might retain their overcoats and keep them in a dedicated officers' baggage wagon, but there was a risk involved:
(July 31, 1863 letter of Lt. William F. Baugh, G/61st Virginia) The wagoner lost my uniform coat, overcoat and all my blankets [the wagon was probably seized or destroyed by the enemy during the retreat from Gettysburg].
Overcoats were expensive:
(Autobiography of George P. Metcalf, D/136th New York) [late 1862 or early 1863] He was charged $13 [a month's pay for a private] for a lost overcoat, plus $2.50 for a lost army blanket.