Hey fellow Final Fantasy X enthusiasts! When it comes to side quests in the game, there are a few must-do activities that can really enhance your gameplay experience.

1. **Monster Arena**: Challenge yourself by capturing and battling monsters to earn rewards and unlock powerful items.

2. **Celestial Weapons**: Each character has a unique ultimate weapon to unlock. Be prepared for some challenging mini-games and battles to obtain them.

3. **Dark Aeons**: After defeating Sin, powerful optional bosses known as Dark Aeons appear. They provide a tough challenge but defeating them yields great rewards.

4. **Blitzball**: Take a break from saving Spira and dive into the underwater sport of Blitzball. Recruit players, level up your team, and compete in tournaments for exciting prizes.

Remember, side quests not only offer valuable rewards but also add depth to the game’s world. So, don’t rush through the main story and take your time exploring everything Final Fantasy X has to offer!