Bottled bleach can last significantly longer than a few weeks hen stored in an airtight container. Supposedly the chlorine solution instructions I found and adapted above will give you something approximating bottled bleach. I haven't tried it though. I have a number of tried-and-true disinfection methods available. This one is meant to be last ditch, or for very large quantities of water, or to disinfect a large amount of surfaces.

In other words, it's not too heavy, bulky, or expensive to include in my big kit.