If anyone wants to try the 100%, here are the list of things to do:

• Complete all 41 main missions
• Win the 18 races
• Win the Demolition Football
• Firefighter (20 fires on each island)
• Paramedic (level 12)
• Vigilante (20 criminals on each island)
• Taxi Driver (100 fares)
• Collect 100 Hidden Packages
• Complete all 21 Rampages

Here's a printable list: https://docs.google.com/document/d/1USFpWKTaE6sk-5XKHCNA9FXRrpqKV-InGvtIpZe1AgA/edit?usp=sharing

Like most other 3D-era GTAs, Advance uses a progress point system for determining percentage completed. Theres a total of 64 progress points(giving 1.5625% each). Points are awarded as follows:

• One for each mission for a total of 41
• One every 25 packages for a total of 4
• One at 10 and 21 rampages for a total of 2
• One every 6 races for a total 3
• One for demolition football
• One for paramedic
• One every 50 taxi fares for a total of 2
• One for every island vigilante is completed on for a total of 3
• One every 30 vigilante arrests for a total of 2
• One for every island firefighter is completed on for a total of 3
• One every 30 fires extinguished for a total of 2

Wow so I'm not the only one playing this game 14 years late? Lmao