For sound effects I use these websites:
incompetech.com, soundsnap.com, storyblocks.com, epidemicsound.com, freesound.org, pixabay.com, mixkit.co
You can find sound effects and music directly on itch.io by visiting the website:
/game-assets/tag-sound-effects
/game-assets/tag-music
I really like these songs:
https://dos88.itch.io/dos-88musicpack