Sand and ziplocks gives customizable weight system. I usually wrap the bags in towels to keep the weights from shifting as well as evenly distributing the weight. If you start doing a lot of weight I would go to a second hand store and get a old down vest that is quilted. If you make a slit at the top of the quilts you can pull the down or fill out and add the baggies of sand, just tape up the holes. I did this to get into shape for a firefighters exam in which you had to wear a 50lbs vest while you completed the course.