I just printed out the code that they sent you in your email. Take that with you to immigration and also take your passport and your boarding pass. That’s all you need. You’re good for multiple reentry unlimited. For the next five years. When you go shopping and use your credit card, bring your passport and of course your Visa card. Very limited places to use American Express. 
holy cow that’s a lot. They just ask for my bank statement to make sure I had $15,000 approximately in the bank account. I’m glad they didn’t ask for pay stubs because I take a draw. Then they came back and asked me for my last year’s income tax return