Not a lot for me as I have simple taxes. I work for companies large enough that they report their workers salaries to the government. And we have a system so that is automatically uploaded to the online tax form the government offers for free for people to use.
Most everything gets reported there automatically for me. As I'm also with mostly major banks - they have to upload my interest earnings and my health care provided also reports that I'm a member
As someone with one lum set of stocks given by my grandmother years ago. They also get reported straight to the tax office and is refilled on your taxes. I think at this point it gets complicated if you have a business, and assets. Especially overseas assets.