Since the resource list doesn't seem to up yet, I thought I'd throw some game dev resources.
Freesound.org offers a massive collection of sound effects and music. Licensing applies but most effects fall under creative commons or public domain.
As for music, there is a page known as nosoapradio.us where you can download a collection of like 500 royalty-free tracks by the artist Deceased Superior Technician. I've used music from that collection in multiple projects. That link goes to a facebook page, so you'll have to scroll down a little for the download. All songs are free to use provided they get proper attribution.
Textures.com is my goto resource for seamless textures and pbr materials. You get a limited number of free texture downloads per day, but its still a great resource.
As for reference material, it might be worth taking a look at gifcities.org and cameronsworld.net. Those sites arent suitable for actual game resources, however they can be used as a reference of sorts to help nail that old internet aesthetic if thats what anybody is aiming for.
For new devs who want to try their hand at using Unity Engine for this jam, the Youtube channel Brackeys offers up some of the best beginner-friendly tutorials.