When traveling within the US I just carry what I normally do on a daily basis.
It may have been overkill but I had four cards plus a debit when I took my first trip to Europe earlier this year I didn't want to risk being stuck without a working card and after seeing that happen to another workshop attendee in Lisbon I'm glad I had extras.
2x Visa
2x Master
1 debit
Two of the cards have high limits so one was hidden in my luggage back in my hotel and one was kept in my wallet in case of emergency.