The Muffin Cart is a small 3 wheeled motor bike that Largo appropriated in some manner and has subsequently kept as a transport and weapon. It seems likely he stole it as the best opportunistic weapon available when he witnessed Dom threaten Erika. He has since used it to clear otaku from MegaGamers, to transport computer equipment to Erika's Apartment, and to plow his way through a crowd.
The Muffin Cart first appears in Chapter 6, as Largo's weapon of defense against Dom as he uses it to run Dom over and remove him from Erika, starting in Strip 665. He continues to use it, adding a rabbitt disguise, to discourage otaku from mobbing Erika, which she resents in Strip 671. He leaves it adjacent to Junpei when Largo decides to help Erika from Meimi Sonoda. Although it would appear he abandoned it to accompany Erika to NIA Hamburger, Strip Strip:682, it's subsequent appearance implies he took it when he retreated after Erika's accusation.
The Muffin Cart makes a surprise appearance in Chapter 7 in Strip 791 with a dramatic entrance as Largo again intervenes when Dom threatens Erika. He also routes the fanboys from MegaGamers, this time with her permission. Ping pulls Miho out of the cart's path, and when she subsequently drops her, Yuki's first Magical Girl act is revealed. When Erika leaves for a quiet walk, Largo takes the cart with him.
The only appearance and mention of the cart in Chapter 8 is when Largo uses it to transport his computer equipment to Erika's Apartment, to test her new computer. While it is known he left his computer behind, it isn't clear whether the muffin cart was abandoned there, too. It is speculated that Piro was about to ask to borrow it in Strip 1025.
Mentioned in strip 959: The weight of my equipment reduced the performance of the muffin cart.
Largo uses the muffin cart to transport himself from MegaGamers to Ikebukuro, where Kimiko is having an event. He does this to defend them from zombies, and along the way picks up Yuki. He then uses it to plow his way through the crowd in front of the event.
Largo named his cart scoot3r of aw3some in strip 1190.