Prepared food, raw food, no difference, it gets taxed, even farmers market vendors are required to collect sales tax applicable to the jurisdiction they are selling in. "On Farm" sales however are not taxed.
Basically Oklahoma expects sales tax to be collected anytime goods of any kind are exchanged even flea markets and yard sales.
They are really going after internet sales tax collection of late. Amazon has caved and collects taxes. Only problem is they collect taxes applicable to the city closest to me but I do not actually live inside city limits so should not be hit for the city sales tax, only county and state.