https://www.pcgamer.com/fortnite-adds-rideable-shopping-carts-reactivates-self-refund-feature/

As teased yesterday, Fortnite's first unlikely vehicle has arrived. Found scattered around the map in various locations, Shopping Carts can be pushed around or ridden as a passenger—both in pairs or on your lonesome. And, yes, players can fire weapons from within the trolley should they desire.  

Shopping Carts are exclusive to Fortnite's Battle Royale variant, and, while they look something like this in my mind, they actually look like the following in practice. Thanks to YouTube person Niovo.