While not strictly a 'side quest,' finding all weapon upgrades and attachments is an essential optional activity that significantly improves your combat effectiveness. These upgrades, such as extended magazines, scopes, and stocks, are often hidden in locked areas, safes, or require solving minor puzzles. For instance, the Dot Sight (Handgun) is found in the Downtown Safe, and the Tactical Stock (Shotgun) is in the Subway Office. Collecting these allows you to customize your arsenal and gain an edge against the relentless hordes of zombies and Nemesis. Prioritize finding upgrades for your most used weapons.
