The MonkMakes Project Box for Raspberry Pi contains all the components needed, together with easy to follow instruction cards, in order to complete 10 simple projects involving LEDs, thermistor, phototransistor and switches and is an ideal starting point for anyone new to electronics and the Raspberry Pi.
This kit is an improved and updated version of the now retired Electronics Starter Kit for Raspberry Pi
A 40+ page booklet by Simon Monk (author of the Raspberry Pi Cookbook and Programming Raspberry Pi) is free to download and explains how to use the kit and build the projects.