Vintage US Military (?) Tan Canvas 8 x 14 x 2 inch pouch with brass snap flap closure and brass belt clip

Looking to ID this bag. I have had it forever and just re-discovered it in my shed. I had always thought that the letters M S G meant that it was a messenger bag, but now that i really look at it, i am not sure that it even is M S G. Canvas is very heavy duty. Has brass grommets for air or whatever on the bottom.Appreciate any help. Thanks.