Is the Wallet/Apple Pay app still on both devices? If so first do a simple reset on the phone (hold power button until OFF slider comes on screen. Slide to power off. Wait about a minute or two then power back on) Check wallet app on phone to see if your cards are back. On your phone go to watch app>my watch. Scroll down to Wallet and Apple Pay. Tap on this and make sure your cards are listed. I don't know your knowledge level on this so if you've done this already don't be offended. Many years of using electronic devices has taught me to start with a reset. That solves 90% of all issues. If that doesn't work I'm afraid you'll have to reenter your cards.
Wallet is built-in on the watch but can be removed from phone so you can't accidentally delete it from your watch.
Which watch and phone do you have? Are you on the latest iOS on both?
I guess, it kind of depends on where you live. I live in London. As you can imagine being one of the biggest and busiest cities in the world, technologically it’s kind of always at the forefront. So it works conveniently for me.