Quantity   Component name
1 × 315Mhz or 433Mhz transmitter/receiver pair Depending on what's allowed
2 × ATtiny85-20SU Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers
1 × USB-A or SMD micro-USB connector For the receiver
2 × 68ohm 0805 SMD resistor For USB data lines
1 × 1.5Kohm 0805 SMD resistor For USB D- pull-up
2 × 3.6V zener For USB data lines, SOD80C package
2 × 1Kohm SMD 0805 resistor For LED/buzzer on the receiver and only LED on the transmitter
2 × LED, 0805 package Fiber Optics / Emitters, 0805 package
2 × 10uF capacitor, 0805 package For transmitter and receiver
1 × 100nF capacitor, 0805 package For the receiver
1 × SMD button For the receiver
1 × CR2032 battery Can also power via broken out pins
1 × Through-hole CR2032 battery holder
1 × 2x4 through-hole 8mm female pins
1 × 1x2 through-hole male pins
1 × ISP programmer I used an USBasp, but anything is good really...