There are many ways to generate a things to do-list in Gmail. Is use this one in which I use only the subject line to describe my tasks. And here's a to do list that will help you to use it too.
1. Make a new contact email@example.com. See also this message. As a contact name, choose an easy but unique set of keystrokes. Something like 'qqq'.
2. Make a label. If you want it top of the label list, use some special signs. I use [ plus ] plus 'to do':  todo.
3. Make a filter that attaches this special label to all mails sent to firstname.lastname@example.org. Also let these messages skip the inbox.
Now start using your to do list. Use shortcut keys!
1. c (for 'compose')
2. qqq + Enter (for getting the address in the To-field)
3. Tab (to go to the subject line)
4. Write a subject line like 'call the dentist for an appointment' or 'return my library books'
5. Tab + Tab + Enter (for sending)
If you don't have a signature, Gmail will ask you if you really want to send an empty message. So, make a signature, for instance just with something like --.