The spare tire, jack and lug wrench for a Mercedes-Benz Vito are typically located in the floor of the trunk, under the panel that forms the load floor. To access them, you may need to lift up the mat and remove the cover. There may be additional tools as well, such as a screwdriver or chocks.
Note: In some cases, especially for smaller vehicles, the spare tire may be mounted on the outside of the car. If you cannot find the spare tire in the trunk, check the underside of the car for a place to mount the spare tire.