For Blueprints, you can use comment nodes as a todo or reminder system. Pick one or more ‘tags’ to use, and prefix a comment with them (e.g., TODO: Spawn FX when shot or FIXME: Convert this constant to a damage curve), and use Ctrl+Shift+F to do a global search in Blueprints for TODO or FIXME or whatever. It will even find the comments in unloaded Blueprint assets.
You can also place Note actors in the level editor, but I don’t know if there is a quick/easy way to find and list all of them (typing Note in the World Outliner seems to work, but will only show them in the current loaded level).
Cheers,
Michael Noland