This may seem silly to some but I have a spreadsheet of every single mod I bought and installed. It lists the mod, where I bought it from, the total price of it, when it was installed, who did it (me or mechanic), and cost of install.



I like keeping records of that stuff so if one day I decide to sell the car, I have it completely documented. Its also good to see how the car has improved year over year since I bought it. One day I may even start keeping track of the performance and horsepower/torque so that there's an upward curve of how great the car has improved.

 

I have a build thread, performs the same task mostly. It does come in handy when you need to check things.