Vehicle system including foot-deck-based vehicle and seat accessory structure

A vehicle system, comprising:

• a foot-deck-based vehicle, including:
• a foot deck, positioned to support a user, wherein the foot deck includes a first handle structure receiving feature;
• a handle structure that is detachably connectable to the first handle structure receiving feature, so as to be positioned for gripping by the user when the user is standing on the foot deck;
• a plurality of foot-deck-based vehicle wheels positioned to support the foot-deck-based vehicle for rolling on a ground surface;
• and
• a seat accessory structure having a seat body, wherein the seat accessory structure is detachably connectable to the foot deck so as to form a seat-based vehicle in which the seat body is positioned to support the user, wherein the seat accessory structure has a second handle structure receiving feature thereon, wherein the handle structure is detachably connectable to the second handle structure receiving feature, so as to be positioned for gripping by a secondary person when the secondary person is urging the seat-based vehicle to roll on the ground surface while the user is seated on the seat body,
• wherein the seat accessory structure includes at least one seat accessory structure wheel that is positioned to cooperate with at least one of the plurality of foot-deck-based vehicle wheels to support the seat-based vehicle for rolling on the ground surface,
• wherein said at least one of the plurality of foot-deck-based vehicle wheels make up a first subset of the plurality of foot-deck-based vehicle wheels and wherein the foot-deck-based vehicle includes a first mounting surface and the seat accessory structure includes a second mounting surface that is engageable with the first mounting surface to detachably connect the seat accessory structure to the foot-deck-based vehicle, and wherein the first and second mounting surfaces are positioned such that a second subset of the plurality of foot-deck-based vehicle wheels is raised off the ground surface when the seat accessory structure is connected to the foot-deck-based vehicle via the first and second mounting surfaces.