Is it permissible to give Zakat al-Fitr from a bag of food that was gifted to me and is more than my need, knowing that I am able to buy it with my own money?

There is no harm in giving zakat al-fitr from a gift, for the gift is the property of the recipient, who can dispose of it as they wish. Scholars have stipulated that if a poor person receives an amount of zakat that exceeds their needs and the needs of their dependents, they should give zakat al-fitr from it. Sheikh Ibn Baz holds that a poor person should give the zakat of their person from the zakat they received if the donation reached them before Eid.