I usually do my scribbling within Logic or GarageBand or whatever. If I get lyric+chord ideas and I don't have access to a DAW I'll open up a text file, jot out some lyrics (usually with a lot of placeholders) and write the chords above.
I've found that if I have an idea which involves a specific sound, it never comes out right, but if I just have a vague sketch of a musical idea and I let the sound emerge from it as I go, then it comes out much better. It's like the music wants to be made on its own terms.