I was in Sweden in 2015 and I didn't need much cash.
- I used Uber for local transportation.
- I used my credit card to buy my train ticket from Stockholm to the airport.
- I used my credit card to pay at the restaurants. (no tipping)
- I didn't buy souvenirs or street food.
- I didn't use a public WC so I don't know about the need to pay.
That's not to say that I didn't carry any cash, I just didn't really need it.