Many containers have perishable products; they're in "reefer" (refrigerated or frozen) containers running on ship power (and dumping heat into air ducted to those refrigeration units). If you've had New Zealand apples or lamb - or fruit from Central America - it likely got shipped this way.

Gotta wonder what's going on with these cargos.

And if you're curious what life is like for the folks working on the boats, check Bryan Boyle's YouTube channel https://www.youtube.com/channel/UCvWe3bMhEXz57UmuSBDLmFQ