I cut the ends off of plastic tubes and sometimes even bottles. The old kind of metal tubes were far more thrifty because you could squeeze them dry (or use one of those keys described above). There definitely is a few days' use left in them. If chopping them up, rolling or squeezing makes the bathroom look untidy, you can run the back of a comb along from the bottom towards the opening to salvage the last bits.
And washing up liquid, shampoo, bubble bath and shower gel are helped out of the bottle by adding water.
I'm not miserly, but it seems common sense to me.