Introduction into a custom backpack system?

Greetings. I'm not sure where to begin. I've looked on the wiki for a method of using tools without the backpack. Essentially, I've disabled roblox's default backpack to use my own instead. I'm asking how we would then make tools still pop up on a player like normal, but just using our own backpack system. How would a normal tool achieve this with the backpack system, and how could I replicate this in a sense.