I was just there for a week. I took out 12,000 pesos from the ATMs and didn't even need half of that amount. I was able to use my visa and mastercard everywhere though in BA many merchants will ask for ID (and would not accept photocopies). So I really only used cash for restaurant tips and taxis. Both are dirt cheap by US standards so not much cash needed. And you can mostly rely on Uber around BA.

My USA passport card has worked for me as ID in such situations. I don't like to carry the passport book if it's not required.

I never carry my passport with me if I don't absolutely have to. On the rare occasion I'm asked for ID, I just show my driver's license. This is really just a bureaucratic formality that pops up sometimes in Latin America, but 99% of the time, the person asking for ID doesn't really care what you present. They just want to note down a number to tick off a box. If it looks official and has your picture on it, you're fine.

Normally I would carry my drivers license but in BA and Rio I was advised to leave my wallet in the safe and just carry a money clip with cash and a couple of credit cards. I had no trouble using my California DL when asked for ID in Buenos Aires. But maybe it is time to start carrying my passport card - which can also be used to meet the TSA 2020 real ID requirements.

Argentine law requires merchants to check the buyer's identity when processing credit and debit card payments. This is usually enforced in larger stores (supermarkets, retail, etc.) and very rarely in restaurants. They don't really need a specific type of ID (the law doesn't state it) -- anything that is government-issued, is written using the Roman alphabet and has a picture on it will do.

Election is on the 27th October but if a run off is required a further vote will be held on the 24th November. Winner needs a either 45% of overall vote or 40% if 10% above nearest rival in the first vote.