What kind of registration do you mean, do you mean as a corporation or LLC? As a fictitious business name? For a city business license? For a state trademark? For a federal trademark? For a domain name? For a federal tax ID number?
Please see the legal guides linked below on operating a small business, then hire a lawyer to make sure you do this right.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
If you are "selling food," you probably are required to obtain food handling permits and comply with County Department of Health requirements. You may want to anonymously contact your County's health department and ask a few questions.
Attention: This response is based upon general legal theories and may or may not specifically address issues that affect your individual legal matter or situation. It should not be relied upon outside of the jurisdiction(s) in which the attorney is licensed to practice as each state has different laws. Each situation is fact specific and requires comprehensive legal evaluation following a thorough consultation and review of all the facts and evidence available. This response does not create an attorney-client relationship between the asking and answering parties.