I have a weird thing about finishing the last drop of shampoo, conditioner, soaps and hand wash because I feel otherwise its wasting money.
I have long hair so get through a lot of conditioner and always cut open the bottle to get the last out. I will add a bit of water to the end of a pump hand wash. Keep using the soap little bits until there is none left.
I've never done the maths on this (I should really) but my guess is that even over a life time, the saving is going to be pence or a few pounds. The last bit of condition in a bottle would probably be about x50 (guessing) to make a whole bottle.
Contrsting, I cheerfully waste money on Starbucks.
No idea why I have this soap related fixation. Anyone else have similar money saving irrational foibles?