If there’s a 3D printer, I think a miniature of the Boing Boing Happy Mutant Mobile should be one of the presets.
A 3D scanner (perhaps photo booth style, could be folding/tent) would be a nice companion to the 3D printer.
When I read unicorn horn soft serve, I thought the unicorn’s horn would be the cone dispenser.
Maybe an ice cream truck style sound system with music box versions of music featured on Boing Boing, or ukulele versions of classic ice cream truck songs—robotic ukulele player? Or some sort of passenger seat PA/radio/webcast system, possibly with a mounted or glove compartment ukulele.
Pull a trailer with couches, theater seating (for watching whatever integrated screen, as others have suggested), or a bouncy castle. Possibly folding for a smaller trailer.
Something passively interactive on the exterior that can be used when the van is parked, even if it’s not “set up”, e.g. a book exchange library or free store in an unlocked display case in the side and rear doors.
