I just replaced my push-to-talk switch—again I keep it and the portable intercom I bought many years ago in a special bag within my flight bag. The portable intercom runs on 9-volt batteries or via a cable connected to the cigarette lighter. It and the PTT have saved many flights when the yoke-mounted PTT failed. If the learner can’t hear the CFI or vice-versa, the flight doesn’t happen.
Headsets are another item that can fail and create communication issues. After the mic on my David Clarks failed, I invested in a backup headset. Acquisition was easy. Hang around at a general aviation airport, and you will likely find someone or someone who knows someone who has an old pair of (insert brand here) that they are no longer using because they have upgraded or are hanging up their wings. The spare headset can become the one you provide to your passenger. They can often be acquired for low cost or no cost. It might need a little cleanup, such as new ear seals, but that is a relatively easy thing to do. Test the headset before you need it, either in the aircraft with the master on or take it to the avionics shop if there is one on the field.
