Kettlebell or mace alternative for travel or at home
During kettlebell exercises, you need to counterbalance and stabilize your body, which leads to improved core strength, balance, and coordination. The HydroCore Bag pretty much does the same thing and probably even better. Using water to fill the bag about half way, not only does it add weight, it also creates a lot of instability as you do the exercises. At the end of a movement when you stopped moving, the water inside the bag continues moving and cause a secondary force that you need to stabilize. This is basically how the HydroCore improves balance, strength, and power.
Unlike the kettlebell, the HydroCore is great for travelling because you can simply remove all the water and pack in the your bag.