This is really just the one script here.
ConveyorBelt.cs
Essentially the collision checking just ensures that the item colliding with the conveyor belt is a valid rigid body, corrects a few edge cases, and then adds them to a list. Then later in the script I iterate through every entry on that list and move it according to the conveyor belt's stats, such as movement speed and direction. It also handles clearing items off of that list once the item falls off the belt.
BeltSpeedController.cs
This script just controls and updates the speed of the animation on the conveyor belt to keep in in sync with the speed of the script.