What is everyone thinking of doing to their cars once they have finished their builds? Aside from the obvious engine upgrades of course

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My plans so far are to looking into a much more accurate fuel gauge system, which weighs the fuel tank, instead of using a float inside the tank.
And to have a look into making heated bucket seats, potentially using thin copper pipe (possibly brake lines?) embedded into some thin padding and running a water pump to pump hot water from the engine through the seats.
I originally thought about using electric blanket style material, but i could see that all going wrong if it rained
At the minute these are obviously just ideas.
Simon