http://www.computerworld.com/article/3064305/android/11-ways-to-get-the-most-out-of-google-keep-on-android.html
7. Turn any note into a list
“Speaking of lists, you probably know you can start a new list by tapping the list-like icon in Keep’s floating action bar — but did you know you can also convert any existing note into a list with a couple quick taps?
While editing a note, touch the plus icon in the lower-left corner of the screen and then tap “Checkboxes.” That’s it; you can now check this off your list.”