Tourist question: Is it necessary to carry some local currency in Amsterdam, Bergen, Oslo (Norway), Iceland and Copenhagen?

Hi, I will be visiting the above cities for 2 weeks, mostly in Norway and Iceland.

Concern:

My local money exchange requires me to exchange about USD100 minimum, and I heard in some Europe countries, you MUST HAVE physical cash, and ONLY because you need to use the toilets. So if I ABSOLUTELY need even $1 in these countries currency, I will need to spend the following:

USD 100 (Copenhagen)
USD100 (Norway)
USD100 (Netherlands)
USD100 (Iceland)

Can someone advise me if euro can be used, if I must give physical cash in these countries?

Thank you!