Unlock the following weapons/equipment by performing the corresponding tasks:

WEAPON/EQUIPMENT -  HOW TO UNLOCK
Bandanna - Complete a single-player session without killing anyone (including bosses). You can do this on any difficulty
Desert Eagle, Long Barrel - Earn the fox emblem on a single-player session
Digital Camera - In the nomad vehicle during the mission intermission; you can unlock a special photo by picking up this item in stage 4 instead of earlier
Patriot Future Assault Weapon - Earn the big boss emblem on a single-player session
Race (Ricochet) Gun - Clear the single-player game once
Rail Gun - Beat crying wolf
Scanning Plug S - Log more than 10 hours of metal gear online play time on the same profile as your metal gear 4 game. You purchase this from drebin.
Solar Gun - Collect the five statues (those of the 4 battle beauties and the frog soldier/haven troopers in stage 1) using non-lethal means on their respective idols
Stealth Item - Complete a single-player session without instigating a single alert (caution is okay, but not alert). You can do this on any difficulty.
Thor 45-70 - Earn the fox hound emblem on a single-player session
World War I Pistol - Earn the hound emblem on a single-player session