Many of the moonwalkers wore strap-on pockets during the EVAs.
At the time this picture was taken, Charlie's training suit was displayed with shin pockets on both legs. The straps that go around behind the leg are visible on the pocket on the right (left leg). Note the four strips of Velcro hooks on the outside of the top flap on the pocket on the right leg.
With the top flap open, we see the strip of Velcro hooks on the front of the pocket which mate with one or both of the strips of Velcro pile on the inside of the top flap to keep the flap closed.
This view of the left leg shows strips of Velcro pile just above the knee which mate with the strips of Velcro hooks on the outside of the top flap to keep the flap open when necessary.