Watts has the Angelo card and the rest of his deck is pretty average, so you should at least be able to beat him. There is also the opportunity to acquire the Quistis and MiniMog cards in Balamb Garden.

If you need to expand your deck and you cannot yet beat opponents, have Quezacotl learn Card. This ability enables you to transform enemies into cards once you have beaten them down to low health. Some common enemies will transform into rare cards, but this will happen very infrequently.