Sandbags are a useful addition for any strength-based training and a staple in strongman sports - here's one way of making them:
- heavy duty garbage bags - the plastic-woven bags you use for chunky construction waste. I heard that in the US duffel bags are so cheap that you can use them, but that's not the case in Germany.
- wood pellets - the kind of pellets that are used for heating. Actual sand would a) leak and b) be too dense, resulting in too small of a volume for the regular sportsman. Highly advanced strongman will have problems to build bags with enough weight with wood pellets, of course, but they are not the target audience here...
- zipties - two to three for each bag
- duct tape
The building is pretty straightforward: Fill the bags with the wood pellets to your liking, leave a little space when you close them with the zipties, so that they won't burst immediately when placing them down, close the zipties themselves as tightly as possible. Cut off the unneeded plastic endings of the zipties and cover the zipties with a few layers of duct tape.
Regular heavy duty bags should hold a maximum of around 60 to 70kg when built this way. Enjoy.