What did the soldiers in the Civil War sleep on?

During most of the war, during the warm months they slept on the ground. The warm months, from about April to December, were "campaigning season", and the armies would maneuver and fight battles. This meant the soldiers frequently walked or fought all day. If a battle lasted several days they "slept on the field", as best they could, amidst the dead and the wounded, who frequently screamed until they too died. Many men would spend the night, searching, shining the light of a borrowed lantern into the faces of the fallen, looking for missing friends or relatives. Sleeping on the battlefield was also called "sleeping on our arms", arms being weapons. The point was to be ready to resume the fight as soon as it was light enough to see. Men were often so exhausted by the exertions of marching and fighting that they did manage to sleep on the battlefield, despite the horrors.

Many men went off to war in the first months with a ridiculous amount of equipment. Often this included tents and camp cots. As the action heated up and moving became more common, and needed to be done quickly, men soon learned they had to discard most of this paraphernalia, whether reluctantly or gladly. One day the tents would be loaded in a quartermaster wagon and driven off, and they might not ever see them again, or if they did, it would be when the armies went into "winter quarters" to ride out the cold months before campaigning season came again. By 1862 most soldiers were down to their rifle, bayonet, cap box (for percussion caps to make the rifle go off when the trigger was pulled), and their forty rounds of ammunition (40 "bullets"), which was what most men usually were issued. If heavy fighting was expected, they might be issued sixty. Some men had a cartridge box, worn on the belt like the cap box, to hold this ammunition. If they had no cartridge box they distributed it in their pockets. They carried a rucksack, slung on a strap over one shoulder, to carry food in and any few personal items they were still trying to keep with them. And they had a blanket roll. This was one blanket, sometimes two if the soldier was lucky, and if he was very fortunate an oilcloth the same size as the blankets. You put the oilcloth on the ground to keep out moisture. You might get with a buddy, if everybody just had one blanket, and use one blanket over the oilcloth (or on the ground it they had no oilcloth) and one to cover up with. There was nothing sexual about this. People at home and even in hotels slept as many to a bed as could fit, and in hotels these would be strangers. In the morning the soldiers rolled up their blanket(s) (and oilcloth, if any) from the foot until they had just a long roll, then folded that in the middle and tied the two ends together with a piece of string. They put this over the other shoulder from their rucksack, and they were packed and ready to go.