Open up a Chase United card. Get 50-60,000 miles after 3 months. Then open a Citi American card for another 50-60,000 miles after 3 months. Now you can fly across an ocean for free about 4 times. Barclays had an American card as well. If you use Southwest or Alaskan, those cards exist too. Check out a site like Doctor of Credit for a whole list.
As long as you pay your balance in full every month and cancel when the annual fee comes due, you can amass a ton of free miles without it costing you a dime. For most nomads, those are way more valuable than some cash back.