I’ve seen cavalry moving in “light marching order” mentioned many times in the course of my research, but not too many descriptions of what this actually entailed. I think the following excerpt by James Larson of the 4th US Cavalry does so rather well.
“Hence the order from the brigade commander was always to move in “light marching order,” which meant that no trooper should carry anything on his horse except what was actually necessary. This order the men of the 4th U.S. Cavalry always carried out more strictly than was really intended by Minty. When stripped for such a march it would be difficult to find an overcoat or extra blanket or clothing of any kind in the regiment. Each man carried only the clothing he wore and, as protection against the rain, only his poncho, which was strapped on the pommel of his saddle. Under the saddle were either two saddle blankets or a saddle blanket and a bed blanket, which served as bed for the trooper whenever time and the condition of the weather would allow him to spread a bad at all, but as no tents or anything to make shelter with was carried, the making of beds depended entirely upon the weather.
“For use in the mess for cooking, a couple of light frying pans were carried in turns by the members, and perhaps also a couple of half gallon tin cups for cooking chickens, ham or coffee, and each man had his little tin cup and knife and fork in the saddle. In the “nose bag” we carried our extra provisions, such as coffee, sugar, salt and whatever we had of bread and meat, so that we were to some extent independent of the pack-mules. We could never rely on them being on hand when wanted. Sometimes we did not see them for several days.
“That was our style in “light marching order” and the style we marched in most of the time during the war. It was very pleasant in fine dry weather, but our condition in rainy and bad weather can easily be imagined. Making the load for our horses lighter was done so as to facilitate our movements, so that we could march quickly without worrying the horses too much.” (Sergeant Larson, 4th Cav., pg 167)
In context, Larson is describing maneuvers trying to bring Confederate raiding parties under Forrest to bay after the battle of Stones River, so this order might be a bit lighter than some others.