mate i think that Phrases is the thing what you looking for
I think the OP is referring to something like the pattern pool concept.
@OP: Renoise doesn’t have that feature currently (that I’m aware of), but you could go about this a different way.
Have part of your sequence dedicated to your song, and the rest to sketching out ideas. Then, when the song is finished and you want to render it, go to “File” > “Render Song to Disk” > “Part to Render” > “Selection in Sequence”, and select the pattern range that makes up your song; that way, Renoise will only render the song, and ignore everything else you’ve done in the sequencer.
I hope that helps.