I used Black Ovis Deer sized bags this spring for my bear. They worked perfectly. Their sets come with 4 quarter bags and a scrap bag. You will also want a bigger bag (Elk sized or whole body deer size) for the head and pelt if you keep it all whole and in one piece.
We have often used Alaskan Game Bags to hang whole deer in one piece in camp. You have to buy the XL size but an average muley will fit in there if you cut them off at the knees and leave the head sticking out.
Two large pillow cases, or a sheet cut in half and then sewn together. As big as a bear can be, they are far from an elk. This years boar I threw one half in one bag, the other in another, it was an easy pack out.