What in-game rewards does buying the physical set give?

I found the LEGO set High Speed Chase, and it says that "Includes unique code to unlock special missions and vehicles in the LEGO City Undercover video game." What missions and vehicles, and are they available by other means?

Take a look here for a look into the LEGO City Undercover code releases

From what I found, the content in the pack unlocks 2 police car chases (for missions)

Chase McCain can hop into his LEGO CITY Elite Police Car and call on his Elite Motorcycle buddy to help apprehend a robber in a sports car! The Police car comes with a special code on the number plate too: enter this code in-game and you’ll unlock two vehicles from the playset and two exclusive car chase missions in LEGO City Undercover

TL;DR If you are strictly looking for in-game content see below, otherwise I have been able to find a purchasable DLC code ONLY in the lego set as described in the OP:

If you take this LEGO game survey you should be rewarded with a key to unlock content.

I also found these that might work (haven't tested them yet) via here:

mhhrhm: Race car driver

xkgzvj: Gorilla suit guy

hvgtpg: Natalia Kowalski

gystqp: WereWolf

N7NN4F9: High Speed Chase Missions & Vehicles Unlock Cheat

3GCC7XR: Justice & Red Sports Car Unlock Cheat

Note: Not all cheat codes can be entered from the Extras menu, exceptions include: A) The mission & vehicle cheat codes have to be entered on the computer terminal outside the Police Station Garage, B) Chase’s disguises & Lego City character cheat codes have to be entered inside the Police Station.

Here is a video confirming the reddit post.