The shampoo bar is good.

Have you tried shampoo bars? They clean just as well as shampoo but don't take up much space, and best of all, they don't produce any waste. Lately, I've been using Donggubat products; even though the quantity looks small, it actually lasts quite a while. Unlike soap, they don't leave your hair stiff, so if you haven't tried them yet, I recommend giving them a try.