US-FAA14 CFR 121.695
Disposition of load manifest, dispatch release, and flight plans: Domestic and flag operations
Read the official ruleOfficial FAA regulation text (public domain)
(a) The pilot in command of an airplane shall carry in the airplane to its destination— (1) A copy of the completed load manifest (or information from it, except information concerning cargo and passenger distribution); (2) A copy of the dispatch release; and (3) A copy of the flight plan. (b) The certificate holder shall keep copies of the records required in this section for at least three months.
Verbatim text of a US Federal Aviation Regulation (public domain), reproduced for reference — not legal advice and not for navigation. A plain-English explainer may be added later; always rely on the current official rule linked above.