Wow, if there was just one cleaning item I could have in my cupboard, it would be Dr Bronner's castille soap. I was recommended this by a friend, (thanks, Rachel!) and will never go back, having tried it, and no, I am not being paid to write this!
Basically, you can get it in the largest bottle, about a litre for around £10. Did I hear a shout? Yes, it does seem expensive, but you have to remember, it is super concentrated, so you have to dilute! Just a little in the bottom is enough, and then fill with water to top, for handwash, and for shampoo, I put a little in bottle, and top with a little hot water, then use immediately on bath nights.
You can also use it for washing floors, sinks...the list is endless. No nast chemicals, and makes lovely lather, too! Just ignore the funny writing on the bottle. The large size lasts an age, even for our family. Plus, there are loads of different varieties, including tea tree, peppermint, lavender, rose.