I’m adding to my previous answer the ruck. The ruck is a backpack that holds some weight in it. It can be bricks, sandbag, kettlebells, weighted plates or books. My choice would be bricks because they are cheap to buy and easy to transport. The reason I like the ruck, is that I can have my clients do a number of exercises while wearing their ruck for extra resistance. They can also go for a run or walk to burn some extra calories.