I have been researching this topic as a treatment for diarrhea, and other similar ailments, while in austere medical environments. My research led me to this YouTube video:

Video

The video (and further research by WHO) led me to order this product from Amazon:

Drip Drop

I have not tried it yet, so I cannot comment on taste. But they seem to have everything needed, and pack/travel well. When at home, I would probably just mix up my own drink, or drink a V8 juice like nursemike suggested (although I would probably drink the low-sodium version, as it has more potassium in it).
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"We are not allowed to stop thinking"