Spending money to save money works if you are smart about it. I pay around £20 a month for my bank account but get free Disney+, free worldwide travel and mobile insurance and free AA cover so it works out cheaper than buying them separately. Only works if you need those things anyway.
Make my own bread - breadmaker £5 off FB marketplace. Also make my own yoghurt and muesli. Control what goes into it so its high quality for less cost than the premium brands. Could make it cheaper if I wanted by varying ingredients.
Take my own coffee, breakfast and lunch to work so never need to buy takeaway anything. Breakfast is overnight oats and lunch is usually batchcooked dinner portioned for lunches.
Buy almost all clothes second hand and try to keep a one-in-one-out system (selling or donating) to make me consider if its worth getting rid of something. Keep slightly knackered stuff for gardening in instead of chucking.
Plan big purchases around sales and maximise offers/rewards/cashback on selling platforms and banking.
Take the coach instead of the train when travelling between cities. Return to London is over £100 on the train or £15 on National Express.
Drive a smaller car with an efficient engine.
Bulk buy where possible - plan storage around this. Non-perishable food, cleaning stuff, loo roll etc. Use bar soap which is bought on offer in bulk - Etsy has people selling boxes of offcuts of fancy soap.
Keep heating low and use heated throws judiciously.
Use a fitness streaming app instead of the gym. Got it discounted through a work scheme.
Had lodgers on and off for years.
Don't eat much meat - use lots of pulses and Tofu for protein.
Most of my furniture is second hand and I upcycle stuff myself.
I am pretty comfortable now so I don't NEED to do much of this but I generally prefer living this way as its more sustainable and I get to save more. Also means I can afford proper luxury stuff when I want it like upmarket restaurants and holidays.