Here are my favorites for those who are still looking for assets:
Art
- https://kenney.nl/assets
- https://www.reinerstilesets.de/
- https://game-icons.net/
- https://craftpix.net/
- https://www.gameart2d.com/
Music
- https://www.bensound.com/
- https://incompetech.com/
- http://soundimage.org/
- https://indiegamemusic.com/
- http://mrjoshuamclean.com/royalty-free-music/
Sound