Hi !
Always using VLC since it has been created.
I would include a functionality, maybe in the right-click on a song of the active playlist, we will could see the option "Play after the current song"
When you click on, the selected song will be played at the end of the active song.
The first song is not end yet and you want choose your third track in your playlist ? Right click on the song you want to heard after the first selected song (not the one who is playing actually) and choose "Put following the selected songs"
I hope you get what I mean because my English is not really good.