An approach used by many small business owners is to assess the various risks in the business and then consult with an insurance broker on the costs of the various coverages . The owner can pick those coverages most appropriate for his business and can buy within the confines of his budget. Clearly, many small businesses can't afford to buy much insurance . As for what insurance your business MUST have, that also depends on the business. Unless some regulatory agency, lending bank, or landlord requires you to carry some form of insurance, you don't have to have any.
Many small businesses operate with little or no insurance coverage.
They are essentially self-insured. If they have a loss, they either cover it out of their own funds, borrow what they need, or they fail as a business. It should be clear to you that there is no easy answer to this question. The best way to determine this is to consult with a business insurance broker . Discuss your needs and obtain quotes for the various types of coverages you want.