Three costs come up in almost every conversation about what a small operation can deduct, and all three have the same underlying answer. They are costs you would have anyway, incurred to put yourself in a position to work rather than in the course of doing the work. That distinction is the whole thing, and once it is clear the exceptions become predictable rather than arbitrary.
Worth going through each one, because the exceptions are real and people who assume the answer is a flat no leave money behind.
The commute
Driving from home to a regular place of work is personal, however far it is and however much you resent it. That is the general rule and it holds for employees and for the self employed alike.
Where it bends is worth knowing precisely. Travel between work locations during the day is business mileage: from the first job to the second, from the shop to a supply house, from a customer to a customer. Travel to a temporary work location outside your normal area can qualify. And if your home is genuinely your principal place of business, meaning the place where you do your administrative work and you have no other fixed office, then the drive out to a job site stops being a commute and starts counting as business travel.
That last point is why the home office question and the mileage question are connected, and why people who dismiss the home office deduction sometimes lose the larger of the two. The two questions answer to the same rulebook, and the IRS material covering them is worth reading in one sitting rather than one topic at a time.
Lunch
Buying yourself food during a normal working day is not deductible, whether you eat at a desk, in a truck, or at a counter. You would have eaten regardless. The fact that you were working does not change what the sandwich was.
Business meals are a different category and a narrower one. A meal with a client or a supplier where business is actually discussed has historically been partially deductible, and the specifics of what percentage and under what conditions have moved around over the years, which is exactly why this is a question to ask about the current year rather than to answer from memory.
Travel is the other exception, and it is the one people underuse. Meals while away from your tax home overnight on business are treated differently from lunch at home, because you are incurring a cost you would not otherwise have. If you travel for work at all, this is worth understanding properly.
The record keeping is what decides these in practice. Who, where, and what business purpose, written on the receipt at the time. Reconstructed at year end, it is an assertion. Written on the day, it is a record.
Work clothes
The test here is unusually clean. Clothing counts only when the work requires it and nobody would choose to wear it off the job. Fail either half and the answer is no.
So flame resistant coveralls, steel toed boots, a hard hat, safety glasses, and specialized protective gear generally qualify. A uniform carrying a company name and logo generally qualifies, because nobody wears it socially. Laundering and maintaining those items is treated the same way as the items themselves.
What does not qualify is the category people most want to claim: ordinary clothing bought specifically for work. A suit for client meetings, a pair of jeans that only get worn on site, boots that are perfectly wearable at the weekend. The test does not ask whether you would choose to wear it elsewhere. It asks whether it is suitable for wearing elsewhere, and comfortable durable clothing is suitable.
The pattern underneath
All three follow the same line. The tax treatment separates costs of being a person who has a job from costs of carrying out the work. Food, clothing, and getting yourself to a workplace are things everyone does, so they sit on the personal side unless something specific pushes them across.
What pushes them across is either that the cost only exists because of the work, as with travel away from home, or that the item is unusable outside it, as with protective gear. Every exception above is one of those two.
What people miss in the other direction
Since this reads as a list of noes, it is worth naming what gets left on the table by people who assume everything personal is disallowed.
The business share of a phone that you also use personally. Home internet, apportioned honestly. Tools of any size, including the small ones bought a few at a time that never get recorded. Professional licenses, continuing education, and trade association dues. Bank and payment processing fees, which for a card heavy business add up to a serious figure. Insurance premiums. And for the self employed, health insurance premiums, which are handled in a specific way that is easy to miss entirely.
When it is genuinely mixed
Most real costs are. The right response is to apportion honestly and write down how you arrived at the split, at the time.
A phone used sixty percent for work is a sixty percent deduction and a note explaining where sixty came from. A truck used for both is a mileage log. A room used for the business and for nothing else is a measurement. None of that is complicated. What makes it defensible is that the reasoning exists in writing and was made when you knew the answer, rather than assembled later from what you hoped it was.