I can only comment on Naples and Pompeii, but this was pre-covid.
We caught a local train from Naples to Pompeii and also Herculaneum. The train was cheap and easy to use. Wear comfy, worn in shoes because there is alot of walking. Hat, sunglasses and sunscreen is a must- plus water. Majority of the frescoes, artifacts etc are all in the museum in Naples, so make sure you go there.
I was warned before the trip to leave any expensive jewellery at home, so I replaced my wedding and engagement rings with a cheap, Claires type band. I know you can be robbed etc anywhere, but had heard of scooter riders coming along and pulling necklaces off etc. We had no issues at all, but my in-laws were robbed at the train station and lost a wallet, phone and tablet.
We looked into walking up Vesuvius, but had also heard stories of the taxi driver requesting more money to take you back to Naples. The thought of traipsing up black, sooty, soil wasn't too appealing either. I'm sure there are organised bus trips, but if you are only there 2 days- I wouldn't entertain the thought.
There was a travel show recently showing people queued up outside the oldest, or most traditional pizzeria in Naples. I don't know the name, and we missed going there, but tripadvisor might be a help in finding it. Have a brilliant time.