Not sure if I'd opt for something as frivolous of an item that could either get trashed and not be reimbursed, or stolen; with the same outcome.
For my personal selfish act, it would have too be something that wouldn't be easily taken away/damaged...
Best bet is a following of sorts... like buy Kishi and add my and others ideas too the mix, too make it less of as "ass pull" no jutsu on the story.. And make it either much longer, or have "many years later" time line introduced, sort of like Dr.Who... (which has been going on for decades btw, lol) same sort of concept for my idea...
...Which might I add, wouldn't be as trivial as a car, because as stated, it can either be stolen or etc, much harder too do either story's (for instance). Then you become legendary in history... And make a nice sum of cash as a long time investment that could span many of your family's/friends lives... (investors) (like a creator of the computer or car)