I have found 2 so far. One I've been able to complete, while the other I'm still not sure how to finish. I am unsure of what the completion rewards are at this time. I have both guides along with videos posted on the discussions page right now.

I have 3 guides on my channel so far (more to come!)
The Jake & Josh Five-seven:
https://youtu.be/LBvsAf-EKfQ

Free PaP Galil:
https://youtu.be/1j_JMDlkUCY

ICE Ammo Mod:
https://youtu.be/cC4r0Y4F_oc

Well that answers the questions on what the game discs do, as for the Galil I had a feeling bout those red lanterns but couldn't put two and two together so neat! Still stumped on the egg roll cat easter egg. Idk what i did but I somehow in one of my game had a B02 navy seal playermodel spawn in the air with the kn44 not far from it. Not sure if it's related to anything.

So completing the Cat egg roll easter egg just simply upgrades your elevator key to the gold variant. Unless there's more to this that I'm overlooking, this just seems like a more convoluted way to upgrade your key. Besides I've still yet to figure out how to even reach the egg roll that goes to the bottom of the overturned building. You don't have enough time to reach it and pick it up.

Heres my eggroll guide cant find a way to do it solo:
https://youtu.be/TPIgWIrDbR8

Do you think these lead to anything or have any significance? These are more things I've found in my runs.

https://youtu.be/Dwp4s7bROyA

https://youtu.be/qcT0myikFlE