Dinki-Di is a quest which will be unlocked soon after the prologue section of the game, when you reach Jeet's Stronghold. It is a fairly straightforward mission where you have to go to Chum's Hideout, recover the dog and Chum's Buggy and then safely bring back the buggy to a stronghold. After it's completion, you get a brand new car.
A new vehicle "Chum's Buggy" gets added to your collection. It comes along with the dog, Dinki Di. The dog is a necessity for clearing out Minefields as he is the only one who can sniff them out. The buggy is also a solid vehicle for off-roading in the trivial stages.