Part of the list is stored in
~/Library/Preferences/loginwindow.plist under the LoginHook key.
Also you'll find a set of LaunchAgents stored in this folder:
Each of the files in there detail a program that is started when your user account logs in.
There's also a similar list in
/System/Library/LaunchAgents that are run when any user logs in, so they're not specific to your user.
In earlier versions of macOS it was also usual to place startup items in
/System/Library/StartupItems. But they're usually not in use anymore.