Supply Caches are wooden boxes scattered about the Two Forks area that contain items which may be useful to Henry. They also typically include a map which will give you additional details about surrounding trails and areas of interest.
There are nine of these smaller boxes in addition to the larger Supply Drop box, and they are all opened using the code "1234" by default.
List of Cache Boxes[ | ]
Cache 241[ | ]
Location: Mule Point Area
Contents: Fossilized Claw, Loose Stone, Note From Ron 6/16/86
Preset Lock Number: 1590
Cache 302[ | ]
Location: Beartooth Point
Contents: Board, Pine Cone (x3), Six Feet Down Under, Note From Ron 7/30/86
Preset Lock Number: 2324
Cache 303[ | ]
Location: Cave 452
Contents: Horn, Flashlight
Preset Lock Number: 6479
Cache 305[ | ]
Location: Jonesy Lake
Contents: Old Sweater, The Fourth Estate, Note From Dave 8/29/86
Preset Lock Number: 9087
Cache 306[ | ]
Location: Nearby Lookout Station
Contents: Granola Bar, Old Rope, Pine Cone, Note From Dave 7/7/86
Preset Lock Number: 8008
Cache 307[ | ]
Location: Ruby River
Contents: Old Toilet Paper (x2), Pine Cone, The Accidental Savior, Jane Eyre, One Chance to Die, Terminal Seven, Note From Dave (No Date)
Preset Lock Number: 2468
Cache 308[ | ]
Location: Cottonwood Creek
Contents: Three Blind Rats
Preset Lock Number: 4321 (try 5678 if you can't open it)
Cache 309[ | ]
Location: Five Mile Creek
Contents: Pine Cone (x3), Missing Person Flyer
Preset Lock Number: 6693
Cache A44[ | ]
Location: Hawk's Rest
Contents: Korea Veteran Hat
Preset Lock Number: 0451