From Longman Dictionary of Contemporary Englishcoolboxcool‧box /ˈkuːlbɒks $ -bɑːks/ noun [countable] 
DFU British English a container that keeps food and drink cool and fresh, used on a picnic SYN cooler American English
DFU British English a container that keeps food and drink cool and fresh, used on a picnic SYN cooler American EnglishExamples from the Corpus
coolbox• Marina had brought a coolbox, and a basket full of food.• A coolbox containing cold packs and energy-restoring, sugary drinks is also useful. 