I always save the first bucketful, before it runs hot, when I'm running a bath or the shower - I can't get it down the stairs without splashing everywhere, so use it to flush the loo a couple of times. It all helps.
My friend leaves all the water there after she has her daily bath, and uses it by the bucketful to flush her loo. It always makes me smile - but makes perfect sense, we really shouldn't be using drinking water to flush the toilet!