Can you afford to play with the budget for a few weeks? I.e. instead of setting a budget for household things tonight, start keeping a notebook of what you spend. Keep a really close, detailed ledger for a few weeks. Catagorize things by groups like "groceries" (actual food,) "household" (cleaning supplies, toilet paper,) "cosmetic" (shampoo, soap, etc.,) "car" (gasoline, oil changes, etc.,) "medical" (otc meds, vitamins, prescription meds, etc.,) "dining out" (including small snacks at work or a candy bar you pick up at a gas station.) Then you can make averages for what you've spent in those weeks, determine where you can be cutting back comfortably, and even start keeping a price book.
If it's critical to start budgeting right now, well, figure out your bills and how much money you have left, allot yourself some of that (but not all!) in cash, and try your darndest not to touch a cent of what's left in the bank for the rest of the week. Do the same every week. And keep the ledger I mentioned above. After a few weeks, you'll be able to determine if you can or should revise your alloted amount a bit. Via that, you'll be able to figure out what you can't live without, and what is truely a luxury or convenience, and set a good, solid budget.
The way I kept this ledger, back when I was vigilant about such things (and I am about to start doing this again) was to take a small-ish notebook that was easy to carry with me (I liked a steno notebook for it's size and top-spiral binding, but I ignored the steno line down the middle of each page.) I listed catagories on the first page, and gave them each a one-letter identifier so I could catagorize purchases easily on the rest of the pages. I divided each page into columns for date, description, price and catagory. I would put the date only at the beginning of a single day. If I went to, say, a grocery store, I would list the name of the grocery in the description column, then start listing every single item I bought (including weight if neccisary,) it's price and the catagory it fit in. At the end of the week, I could review my spending and say "Ok, I see I spent x amount of money on groceries that were really undeniably reasonable (i.e. flour, apples, broccoli), y amount on groceries that were more luxury (i.e. ice cream, canned soup), and z amount on groceries that were serious luxury (cherries in December.)" And I could easily transfer those prices into a price book later.
*sigh* Well, I have a steno book here... I guess I'd better get busy setting it up. I need to get back on track here myself. I'm so good with this stuff in theory... I need to get better in practice