The bottom drawer of my filing cabinet is the designated spot for Primary stuff. I found that a simple alphabetical index system works best for me. I bought large A-B-C-D inserts, as you can see. Each song has a folder with the visuals in it such as flip charts, cut-outs, pictures glued on tongue depressors, etc. If it's a song from another source other than the Children's Song Book, I include a copy of the music, too.
For Posters, I bought two of these carriers. One to store them all in, and one to transport the poster(s) of the day back and forth to Primary. We sit on the side benches in Sacrament Meeting, and this little holder fits nicely against the wall. Love it.