How do I find my 1N 4007 diodes?
While the ArduinoStarterKit page at arduino.cc lists “5 Diodes [1N4007]” as part of it, and has a picture where 5 diodes apparently appear slightly left of center in the top row, several other pictures that come up in a google images search for official Arduino Starter Kit apparently don't show the diodes.  Eg, as at arduino starter kit.  But 4 Best Starter Kits for Arduino Beginners does show them.  

Note, unless you are working with medium to high AC voltages (eg above 50 V) you can substitute 1N4001 - 1N4004 which have lower PIV ratings but also slightly lower forward voltage drop.  For many beginning projects, 1N4148 signal diodes will be adequate and perhaps less expensive.