Unwanted programs at startup

Go to System Preferences -> Users and Groups.

On the left sidebar click on your user name and then Login Items.

In that window you can configure which apps to run automatically at startup (click on + and - at the bottom to add or remove apps).

Please note: many of these apps (such as Creative Cloud or Dropbox) have their own switch. Just check their Preferences to activate/deactivate those apps at startup.

For Dropbox, see screenshot attached: as you can see i have the option "Start Dropbox on system startup" unmarked and (as you may expect) it does not run automatically every time i switch my Mac on.