What should I do with my expired passport?
I recently renewed my passport, and have a shiny new one. When renewing, I sent in the old one as proof of citizenship/identity, but was surprised that, along with my new passport, the old one was sent back - with a few holes punched in it to verify its 'uselessness'.
Most advice I can find re: holding on to expired passports mainly advises doing so in order to use them for the exact purpose that I used mine; but beyond that (since I have a new passport, which will someday be expired), is there any reason to hold on to the old one? If not, are there any particular precautions I should take in disposing of it beyond ensuring that the page with my identity is torn out and shredded/cut into tiny pieces to avoid identity theft?
(If it's relevant, mine is a US passport)
Many people like to save old passports as a souvenir of past travels. Just keep it in a safe place with your other important documents.
I'm not sure what you mean by 'with a few holes punched in it'. If it isn't too obvious that it is void, you might think about taking it with you when you travel to a more dangerous location. That way you can carry your old one for identification purposes without having to worry about getting your actual passport stolen. Especially if it isn't past the expiry yet.
Quite a few countries, apparently including the US, physically mutilate expired passports (clip off a corner, punch a hole through it with a hole puncher), etc to make it completely obvious that it's invalid. This also has the helpful side effect of making it harder for you to accidentally take it instead of your new shiny passport!
It also contains records when you entered and left certain countries. This can be important for immigration or business purposes
Officially the only reason you'll need your old passport is if it contains any visas that are still current - despite being in the old passport these visas are generally still valid. If this is the case, then obviously you'll just want to carry your passport with you.
If you have no visas, then the best advise I can give you is to put your old passport in one of your bags (preferably one of the bags you check-in). In the event that you lose your current passport - especially if in a foreign country - having your old passport will make the process of obtaining a replacement much easier.
Personally I have my previous passport in an envelope containing some spare cash, a spare ATM card, and an old Drivers License. To date I've never needed any of these, but it's good to know they are there if I ever need them!