Colgate sold their shaving sticks with a handy grip, which you could reuse.

But what about the soap that sat in the grip? There is at least half an inch of soap in there.

No need to waste it though:

Just unscrew it and stack it on top of the new shaving stick. And you just got fifty shaves for free.

However; if a half inch of shaving stick gives you fifty shaves, you were only supposed to use up about a quarter of a millimetre of soap each time. And that is not a lot.

I strongly suspect they played up the number of shaves you could save, in order to emphasises the thrifty aspect.