As documentated in "Coffin Contents"
A broken cell phone, a broken MP3 player and a working cell phone from which all memory has been wiped clean. It's possible that the broken MP3 player could reference the runners from "The Runner's Journal".
A heavy lead pipe, a machete and a switchblade. Possibly 1AmTheHelp3r arming Caught against future encounters with either the Slender man or himself. Though the Slender man is seemingly impervious to weapons.
A small jar of water or another thin liquid. Is slightly amber in color. Purpose and origin unclear.
A black journal bearing the same carved in Slender man image. Looks extremely reminiscent to the Runner's Journal given to Caught by RoivasSevil. The inside is burnt but there is nothing written on the pages.
Pink bike tassels.
Many, many tapes. Caught mentions that they include Bob Dylan, The Beatles, and various music recorded off the radio.
The Map, given to Caught before the coffin was opened, stuffed in one of the coffin holes. On the back of the image was written the poem, and on the front is a map of the woods. Caught mentions that woods seem to relate to where he dug up the coffin, which was buried at a spot labeled "Birdies, birdies, birdies" on the map. Much of the map remains unexplored, including an area labeled "Picnic spot", a drawing of Slender man in a corner, and a house with a warning not to venture there. Caught asked if he should search the woods, but it was voted that he instead visit 925 Cranbrook Drive at RoivasSevil's suggestion.
Working Theories and Observations
The small jar is identical to the jar found in Lancing Place. Dubbed "Slenderbane" by viewers, the Lancing Place jar seems to have properties that protect the user from Slender man. RoivasSevil has claimed that the jars contain "the end of what once lived".
Closer inspection reveals the following details/locations
"Birdies Birdies Birdies" Next to an X, possibly "mist" as well.
"Don't go up there friend" next to a house or possibly a coat.
"Picnic Spot" Next to two figures and a picnic blanket.
"Dog trail" or maybe "Dog road".
Possible figure in corner.
"The dog goes _ _ (woof woof or arf arf?)"