Backpack convertible to a stretcher

A backpack comprising:

• an accommodating body having a horizontal bottom wall with front, rear, left, and right sides, two side walls extending respectively and upwardly from said left and right sides of said bottom wall, and front and rear walls extending respectively and upwardly from said front and rear sides of said bottom wall, each of said front, rear, and side walls being connected removably to two adjacent ones of said front, rear, and side walls along two opposite sides thereof so as to define an accommodating space that has an upper end opening, said accommodating body being stretchable such that said front, rear, and side walls are coplanar with said bottom wall so as to form a stretcher, each of said bottom, front, rear, and side walls having an inner side surface facing said accommodating space, and an outer side surface opposite to said inner side surface, each of said front and rear walls having left and right sides;
• two spaced-apart slings fastened to said outer side surface of said front wall of said accommodating body and disposed adjacent respectively to said left and right sides of said front wall of said accommodating body;
• and
• a plurality of sliding plates attached removably to an assembly of said inner side surfaces of said bottom, front, rear, and side walls of said accommodating body so as to contact the ground when said accommodating body is stretched and when said outer side surfaces of said bottom, front, rear, and side walls of said accommodating body constitute a top surface of said stretcher.