If you have access to any old, tire inner-tubes, they work well as a
makeshift sandbag. Tractor innertubes are good, though can be pretty
heavy if they're too large.

First cut it in half. Using 2x4s, fold one end closed and "clamp" it
between two 2x4's and screw the 2x4's together with several wood
screws. Fill the tube with sand. Close the open end the same way as
the other.

An averaged sized agricultural tractor tube cut in half and filled with
sand can weigh over 100 lbs, so be careful, and maybe cut it into
quarters instead of halves.