Regularly when I write my shopping list and it has a lot of the same things on it.
Loo roll, washing up liquid, tins of beans, coffee, tea; to name just a few. I often end up with cupboards full of stuff, mainly bought on offer, but actually I have no idea how long things last for.
So I've tried to be conscious of what I'm doing, for things that can be stocked up on.
Soap powder - I've just opened a new box of soap powder (bought from Approved Foods)so tried to work out how long the last one lasted. I bought gel as it was on offer for £2, and I've just checked back and it was part of a Tesco order on 24th November. Not bad value for money. We'll see how long this powder lasts.
I'm fortunate enough to live in a soft water area, so mainly ignore the instructions on soap powder. I know from experience how much to put in, and have a little tub especially for the purpose. Also, our stuff is not really 'dirty', just not clean enough to wear again.
Making your own laundry products
I've used the last of my home made laundry 'goop', made from a recipe on MSE, and haven't got round to making any more. I've not bought fabric conditioner for years, use white vinegar and/or essential oils instead.
Soapnuts - these get used for things like towels and bedding - things that need freshening up. This helps to eke out the soap powder useage, and does leave things really soft.
White vinegar - I've just bought a new bottle - a huge container really for £1.25 and have made some lavender vinegar to use as a spray for cleaning the loo and the bath, and in a jar in the kitchen I've just started some lemon vinegar (need to remember to keep giving it a shake!)