For this Achievement you have to collect all
17 Battle Journals, all
16 Voice Mail Recordings and all
34 Notes. The 100 Zombie Statues and 30 Flags are not required for the Achievement. You can check in the Inventory Tab (push X here) which Collectible you have collected and which not. Battle Journals and Notes are located on Slums and Old Town, Voice Mail Recordings only in Old Town.
The best Time to collect the 67 Collectibles is after the Story. Choose Continue in the Mainmenu and you go back to Harran in Free Roam Mode and can all do what you want. Another good Hint is, reach Rank 12 in Survivor Tree for the Grappling Hook. This Tool makes the climbing so much easier in the Game.
A Word to the Sidequest, Sidequests unlocks Locations and on this Locations are many Collectibes. For the Battle Journals you have to play 0 Sidequests, for the Voice Mail Recordings you have to play 2 Sidequests and for the Notes are tons of Sidequest to play, so the best Way is, beat the Game, play all Sidequest and then begin to collect the (missing) Collectibles.
Note from Prattalmighty in the Comments:
You may want to also add in a part for the people who were stuck like me with 67/67 collectibles found, but less than 100% showing in the tracker. They can start a "New Game" save file and start picking up notes and battle journals, they'll see their completion percentage rise and the achievement will unlock after a few, work for me today.
Battle JournalsTimeline:
*** Spoiler - click to reveal ***00:16 - #01 - Sewer - Battle Journal Entry #11
01:36 - #02 - Slums - Battle Journal Entry #10
02:05 - #03 - Slums - Battle Journal Entry #6
02:35 - #04 - Slums - Battle Journal Entry #9
03:06 - #05 - Slums - Battle Journal Entry #8
03:38 - #06 - Slums - Battle Journal Entry #4
04:20 - #07 - Slums - Battle Journal Entry #2
04:51 - #08 - Slums - Battle Journal Entry #1
05:20 - #09 - Slums - Battle Journal Entry #7
05:50 - #10 - Slums - Battle Journal Entry #3
06:23 - #11 - Slums - Battle Journal Entry #5
08:20 - #12 - Slums - Battle Journal Entry #0 & #12
09:35 - #13 - Slums - Fast Travel Location to Old Town
10:11 - #14- Old Town - Battle Journal Entry #14
10:47 - #15- Old Town - Battle Journal Entry #15
11:18 - #16- Old Town - Battle Journal Entry #16 (Epilogue)
11:50 - #17- Old Town - Battle Journal Entry #13
Voice Mail RecordingsTimeline:
*** Spoiler - click to reveal ***00:16 - #01 - Voice Mail Recording #9
00:41 - #02 - Voice Mail Recording #10
01:08 - #03 - Voice Mail Recording #15
01:36 - #04 - Voice Mail Recording #5
02:00 - #05 - Voice Mail Recording #16
02:27 - #06 - Voice Mail Recording #4
02:54 - #07 - Voice Mail Recording #3
03:22 - #08 - Voice Mail Recording #13 (Required 2 Sidequests - Rubert the Gunsmith & Health Potion)
04:52 - #09 - Voice Mail Recording #14
05:24 - #10 - Voice Mail Recording #1
05:53 - #11 - Voice Mail Recording #12
06:19 - #12 - Voice Mail Recording #6
06:52 - #13 - Voice Mail Recording #8
07:19 - #14 - Voice Mail Recording #2
07:47 - #15 - Voice Mail Recording #7
08:21 - #16 - Voice Mail Recording #11
Notes Timeline:
*** Spoiler - click to reveal ***00:16 - #1-2 - Slums Note #25, #24
01:02 - #3 - Slums Note #23
01:29 - #4 - Slums Note #2
02:00 - #5-7 - Slums Note #26, #16, #17
02:57 - #8-10 - Slums Note #13, #14, #20
03:57 - #11 - Slums Note #21
04:35 - #12 - Slums Note #19
05:04 - #13-15 - Slums Note #18, #3, #15
06:06 - #16 - Slums Note #1
06:34 - #17-18 - Slums Note #4, #5
07:24 - #19 - Slums Note #11
07:55 - #20 - Slums Note #22
08:25 - #21-22 - Slums Note #7, #6
09:12 - #23 - Slums Note #8
09:48 - #24-25 - Slums Note #9, #10
10:32 - #26 - Slums Note #12
11:51 - #27 - Old Town Note #33
12:18 - #28 - Old Town Note #34
13:10 - #29-30 - Old Town Note #27, #28
14:59 - #31 - Old Town Note #29
15:40 - #32-34 - Old Town Note #31, #30, #32
Required Sidequests and Quest Giver: (Video sorted)
*** Spoiler - click to reveal ***Note 25 / 24 - Steal from a Thief > The Big Bang Thesis > Total Security - Jaffar
Note 2 - O Brother Where art Thou? - Osman
Note 13 & 14 - Tunnel Vision - Ryan
Note 21 - Mothers Day - Automatically
Note 19 - Gassed Up - Automatically
Note 1 - Goodnight Mr. Bahir - Brijesh (Tower 20th Floor)
Note 11 - Voltage - Alfie (Tower)
Note 22 - A Survivors Guide to Zombieland - Neil (North East of the Map)
Note 7 & 6 - Gunslinger - Dawud Tower (20th Floor Room 203)
Note 8 - Wheres My Mother? - Meliha (East of the Map)
Note 9 - Gas Mask Man - Musa (Fishing Town - East of the Map)
Note 33 - Rubert the Gunsmith > Health Potion - Fidan > Rupert
Note 34 - Fan Zone - Noah (Fast Travel Safehouse)
Note 27 & 28 - Do You Believe? > Shadow of the King - Mufid > Ishaq
Note 29 - Chasing Past - Tariq