Grand Theft Auto III - The Definitive Edition

There are numerous guides on the Internet for the locations of the 100 hidden packages  and most aren’t too difficult to collect. It’s recommended that every time you get to a new island you collect all the ones you can as doing so will unlock several rewards including. 
 

• 10 packs - Pistol 
• 20 packs - Uzi 
• 30 packs - Grenades 
• 40 packs - Shotgun 
• 50 packs – Body Armor 
• 60 packs - Molotovs 
• 70 packs - AK-47 
• 80 packs - Sniper Rifle 
• 90 packs - M16 
• 100 packs – Rocket Launcher 

For a guide for all 100 you could use the GTA wiki one found here.