Here in the states, most people use Amex/Costco card as membership cards.

Overseas, some Costco staffs are not used to the Amex/Costco card and some can't use it because it's not chipped and the membership number is very small. So I always bring the white Costco membership card with me when I travel/stay overseas. The white Costco membership card is universal. But I have to pay with local contracted CC or cash.

If you don't have a white Costco membership card, go to Costco customer service desk before your trip and get one for free.