This instable walk with an aqua bag over your head is a challenge for everyone. You can vary a lot with the steps and weight. This is a great way to train your ankles, don't make it so hard you will be left with a sprained sprankle. Make sure you will be able to concentrate yourself and don't do this for endurance.
Depending on the number of balance balls you have you can create a little street upto 10 balls. Don't over do the series upto 50 steps an training is quite enough.