I have an excel spreadsheet to lay out my budget and track my spends. I also track my spends on my online banking - and they have a handy feature allowing you to set budgets for the month for different categories so I have a fair idea how it is looking.
I allow myself up to €800 per month for groceries. This includes alcohol, cleaning materials and also the groceries I get in M&S near work for my desk drawer snacking (fruit, packs of nuts, sometimes crisps, sometimes some sparkling water and an occasional lunch). Many months it is under that, but it means when good deals are on, I am happy to stock up, I have discretion for convenience food when life goes haywire, and also that I can spend a fair amount on Christmas groceries (including all the treats etc) because I have allowed for it. (I spent just over my annual "allowance" last year - which was a particularly bad year for needing conveniences and not doing well with the freezer).
I do the same for petrol (allow for 1.5 tanks per month), as across the year that works out about right (many months are less than a tank, but there are a few months where I have long journeys for work or Scouts or seeing DPs to factor in).
I don't do it for everyday coffees, as I give myself €50 per week for discretionary spending including coffees. But I have a pot for eating out and takeaways.
I have one for clothes, another for stationary (secondary school DD - so it needs its' own pot!), another for books (weakness of mine), etc.
I also have a habit of "paying myself first". Before I even get my paycheque, there is money taken out and sent to the credit union at work on a monthly basis (well, every fortnight, when I get paid). And I also have an SO set up to put more into different savings in the middle of every month (as I generally pay any bills at the start of the month).
And I do try and keep to only spending the €50 per week, covering things like coffees, lunches (I bring salad from home a lot but eat out occasionally too), occasional magazine or bar of chocolate for eating on the train at the end of a bad day at work.....many weeks I still have cash in my wallet at the weekend.
And while I have a large groceries budget, it covers a lot, and as I mentioned includes when we host events at home (dinners or BBQs etc) and also Christmas. I grow some of our own veg (I'd like to do more but both time and space restrict me). I do a lot of cooking from scratch, batch cooking and freezing, and buying yellow-stickered food that we would eat anyway and freezing....and will happily use coupons as well on things we would buy anyway - but also need to be able to have things for when life goes haywire, DD (SNs) is in a controlling phase and won't eat what is planned, or just the general busyness of our lives means we need some conveniences and short-cuts.
I added up my potential for savings this year earlier - if I stuck to that, I could have a large pot at the end of this year. But I know that there are spends I haven't yet allowed for (including holidays, and a realistic amount for DD school/equipment/hobbies costs). But I am aiming to keep spending on clothes for myself as low as possible, and also to reduce the grocery spend at least somewhat this year.