It's a super easy, super quick Joomla task to make your life simpler. Just follow the instructions below to get your 'To Do' list.
Navigate to Extensions > Modules
In the search bar just above the modules list, select 'administrator', rather than 'site'.
Click on New > Custom Module
Give the module a TITLE and choose the POSITION 'cpanel' from the list.
Enter the things you would like to do or remember in the editor.
Change the ACCESS level to 'Special'.
From the ADVANCED tab select '6' as the Bootstrap size.
Click on 'Publish'.
Click on 'Save & Close'.
That's all there is to it, now just go to your control panel and see your new module. All you need to do is update your new custom module as your TO DO list changes.
You can change the ordering of the modules just like you would normally. If you don't know how to do that, you can find out how to change Joomla Module ordering in this article.
***TOP TIP*** If you want to style your new module to match the others, make your entries an un-ordered list and add a class to the containing div. In Joomla's default 'Protostar' template it would look like this.....
<ul class="list-striped list-condensed"> <li>Back Up Website</li> <li>Add More Articles</li> <li>Optimize Images</li> </ul>
Check out the images below to see more.