In the U.S., are credit cards essentially necessary to live a normal life compared with debit cards or cash?

Not really. I know a lot of people who have absolutely shunned credit cards, and live in the US only on cheques and cash, though buying online, etc. can be difficult.

Most people have resorted to adding a debit card for such purposes. Credit cards are not necessary, but debit cards can ease the difficulties.

Having said this millions of people in the US live without have access to banking.