[Paraaronoid]

Can you find any weighted objects in your surroundings to use? Sand, small rocks, etc.??

XS Scuba makes velcro weight pouches that you "fill" with lead shot. They come in different sizes, meant to hold 1-6 pounds of lead. They are not meant to be disposable, but you could use them instead to fill rocks, gravel, etc., whatever has weight in your surroundings, and then dump them out on the way back.

You would have to accept that you will need more volume of weights though, given that anything you use in your surroundings won't be as dense as lead.