A tub was a container used for storage and distribution.

Ice cream was sold in tubs, (PROSE: Most Beautiful Music) as was coleslaw. (TV: The Parting of the Ways, Cyberwoman) During her first encounter with the Eleventh Doctor, while he discovered the wonders of fish fingers and custard in her kitchen, Amelia Pond ate ice cream directly out of the tub. (TV: The Eleventh Hour)