Stock take your fridge/ freezer/ food cupboards before making a shopping list.
Always make a shopping list and meal plan, the days can be flexible but you need to know how you are going use the random packet of quinoa in your cupboard.
I keep a cashbook so I know where every penny goes, it's how we can create a budget, see if we are over/ under budget and work out our long term goals. I have a cashflow forecast set up so I can see where we'll be in a years time.
Credit cards have been excellent for cashback, i use them for everything. I'm on track for £170 back from Amex and have had £40 amazon vouchers from my Amazon Mastercard.
I use receipt scanning apps for cashback too, storewards/ huyu and shopping.
I have every loyalty card if available, sometimes I get offers. I keep them on my stocard app. No-one has space for all of those.
I also use Quidco and have honey on my browser as an online discount code search.
Try to avoid adverts, tune them out. Marketing is really clever but once you stop listening to them telling you that you need XYZ, the want disappears.
Most importantly, don't spend for the sake of it. Follow minimalist blogs. Only buy what you need, make a list of what you want and wait until next payday. You'll find you don't really want it anymore.