I LOVE this question so much and I want to give the right answer, so you will get two! One comedy and one very serious:
Hee Hoo Funny Heist
Breaking into the United States cheese vault and stealing every last crumb of delicious dairy, and leaving a Kraft single in the center of the underground facility.
The Great Gouda Getaway they'd call it! The Haloumi Heist! The Cheddar Caper!
I could go on, but I will cheese it for now~!
Serious Business
Mabel breaks into either Aurora or Bradley Headquarters and takes nothing seemingly, instead leaving a note in spray paint that simply says:
"We know.
Thanks to our little leak,
G."
She purposefully leaves digital footprints all over the supposedly super encrypted files on their drives including financial data, origin information, weaknesses, etc. She doesn't take anything on this trip (this is all data the Korps already has naturally), but just wants to show that she can get in anytime she pleases, and do what my dears?
Sow chaos. Can you imagine the infighting and accusations flying at they try to figure out who the leak is?
GLORIOUS CHAOS!
(I mean she would also take some innocuous to remember the trip by, maybe someone's alternate weapon, or maybe just some fun photos of the embarrassingly deviant pictures of Korps villains in the lockers~!)
