If relates to a current project they go into project support. I keep my project support in OneNote, so if you are having a brainstorm/mind dump you can put them all there. If nothing is obviously actionable, then leave them there and just keep adding more as more thoughts come through. Then you need to allow some time to review all of them together, as part of the project review (this might be part of the weekly review, or part of project time) and see if there is anything you can link together and action.
If it relates to an area of focus, I have AOF support sections to keep this stuff, and leave for your AOF review.
If not a project nor AOF, then it is either reference or someday/maybe.