I don't know much about Mississippi, but I know that in neighboring Louisiana, there are drive-through daiquiri places.

the fine print of the law says that the open container law is not applicable to containers with frozen alcoholic beverage where the lid is intact and no straw is protruding through the lid.

In most cases, daiquiris adhere to the “tape rule.” Most daiquiri shops will put a piece of tape over the straw hold on the lid. If this tape is removed or broken then the drink is considered an open container.

So a piece of tape counts as a "seal." They're not even trying.