No Crate Left Behind

Edit: As this is the top comment, for visibility purposes I'll try to keep it updated every day until we finish this achievement, because Wowhead is so slow to add stuff.

Here we go:

All the crates for Crate Insurance Agent and No Crate Left Behind

1. 
   
2. [item=232263]: Found by a Blizzard hint, in Desolace, you must be dead to see the crate and accept the quest.
   
/way #66 54.0 58.1 Desolace Crate

   
3. 
   
4. [item=226200]: In Zuldazar, buy a [item=225996] from [npc=143029] (on the sea floor) and interact on the shell above her.
   
/way #862 54.2 54.2 Zuldazar Dive Bar

   
5. 
   
6. [item=228767]: Pick up [item=228768] in Thousand Needles then buy the crate from [npc=91079] in Azsuna for 500g.
   
/way #64 66.3 86.2 Underwater cave entrance
/way #64 64.9 84.4 Water-Resistant Receipt

   
7. 
   
8. [item=228322]: In the Karazhan crypts (not in instance). Use the coords below or this video showing path to crate: https://www.youtube.com/watch?v=MxZ5GuOdPlI
   
/way #42 39.83 73.11 Step #1 Crypt Entrance
/way #42 33.52 70.72 Step #2 Go down the spiral tunnel
/way #42 30.22 81.33 Step #3 Swim to the other side
/way #42 22.43 83.74 Step #4 Crate location

   
9. 
   
10. [item=226375]: In Rivenwood, Howling Fjord. Use the [item=208092] to uncover it.
    
/way #117 29.41 6.36 Howling Fjord Crate

    
11. 
    
12. [item=228212]: Underwater, off the coast of Tanaris, south of the Caverns of Time inside a gnome building. Do NOT step on the elevator inside the building, it can and will likely crash your game.
    
/way #71 69.17 68.64 Crate (Underwater Inside Building)

    
13. 
    
14. [item=228976]: In Mount Hyjal, at the base of a trampoline.
    
/way #198 13.6 33.5 Crate in Mount Hyjal, at the base of the trampoline

    
15. 
    
16. [item=231886]: Grab the [spell=463368] in Ashenvale, this gives a 30 min Buff that can only be kept on Kalimdor. You will lose it if you port anywhere else. You must travel via non-loading screen means! Potion does have a ~5 min respawn so if not there hang out and it should come back. Then fly down to Feralas near Dire Maul area and grab the crate.
    
/way #63 47.9 38.4 Potion of Truth
/way #69 60.42 35.40 Mildewed Celebration Crate

    
17. 
    
18. [item=228983]: Inside Oshu'gun crystal in Nagrand, Outland
    
/way #107 35.27 74.81 Crate inside Oshu'gun in Nagrand, Outland

    
19. 
    
20. [item=228770]: First collect the [item=228772] from inside a cave outside Ahn'Qiraj, by the water. Then use them at the Unmarked Grave in Stormheim.
    
/way #12 40.4 93.1 Cave entrance in SW Silithus behind Ahn'Qiraj (not inside instance)
/way #12 40.7 92.8 Summon a dog battle pet (like Perky Pug or Corgi) to dig the Mysterious Bones
/way #634 37.4 47.6 Place the bones at the Unmarked Grave in Stormheim

    
21. 
    
22. [item=229367]: The crate can be found in Maldraxxus on the upper level of the Seat of the Primus, next to the portal that would take you back to the inner area.
    
/way #1536 49.99 73.81 Ghostly Celebration Crate

    
23. 
    

To see which crates have been returned, listed in the order of the table above, copy/paste this command into chat:
/run local s,t={"HAZ","SOG","SAN","DIR","BAT","WAT","CHA","MIL","CRY","SUP","GHO"},{85574,83794,84624,84470,83931,84426,84767,85523,84773,84625,84909} for i,v in ipairs(t) do print(s,":",C_QuestLog.IsQuestFlaggedCompleted(v)) end
Note: There is an alternate version of the #1 crate, which is only available if you did NOT pick up the Desolace crate. It can not be picked up on a character the [item=232263] was picked up on (so if you've been following this guide, basically too late now, must be done on an alt). It can be found at the following coordinates in Nagrand, also while dead (so drop down without armor on from a great height). Release, then click on the [npc=233545]. If you don't see it, you must have already collected the [item=232263] on this character, must be done on an alt.

/way #107 21 60 In Nagrand TBC - Fly up, dismount, die and release here
/way #107 21 57 As a ghost run around the mountain and interact with Curious Haze


Credit: WoW Secret Finding & Collections Discord server, channel #guest-relations-secrets

One big copy/paste for those who like it:

/way #66 54.0 58.1 #1 Desolace Crate (must be ghost to see)

/way #862 54.2 54.2 #2 Zuldazar Dive Bar (buy Clam Digger from Nikto and interact on the shell above her)

/way #64 66.3 86.2 #3 Step 1 - Underwater cave entrance
/way #64 64.9 84.4 #3 Step 2 - Loot Water-Resistant Receipt
/way #630 66.4 40.4 #3 Step 3 - Purchase Sandy Celebration Crate from Vashti the Wandering Merchant (travels on path)

/way #42 39.83 73.11 #4 Step 1 - Karazhan Crypt Entrance (not the instance)
/way #42 33.52 70.72 #4 Step 2 - Go down the spiral tunnel
/way #42 30.22 81.33 #4 Step 3 - Swim to the other side
/way #42 22.43 83.74 #4 Step 4 - Crate location

/way #117 29.41 6.36 #5 Howling Fjord - Battered Celebration Crate

/way #71 69.17 68.64 #6 Waterlogged Celebration Crate (Underwater Inside Building 2nd floor)

/way #198 13.6 33.5 #7 Hyjal Crate in Mount Hyjal, at the base of the trampoline

/way #63 47.9 38.4 #8 Step 1 - Loot Potion of Truth (do not exit Kalimdor or you lose buff)
/way #69 60.42 35.40 #8 Step 2 - Mildewed Celebration Crate

/way #107 35.8 67.4 #9 Step 1 - Oshu'gun entrance, Nagrand-Outland
/way #107 35.27 74.81 #9 Step 2 - Crystallized Celebration Crate inside Oshu'gun

/way #12 40.4 93.1 #10 Step 1 - Cave entrance behind Ahn'Qiraj (NOT instance). Summon dog battle pet (Perky Pug, etc)
/way #12 40.7 92.8 #10 Step 2 - Jump down and go to bone pile behind sleeping Andestrasz, dog will dig, loot Mysterious Bones
/way #634 37.4 47.7 #10 Step 3 - Place bones at Unmarked Grave in Stormheim

/way #1536 49.99 73.81 #11 Ghostly Celebration Crate (upper level of the Seat of the Primus)

Ghostly Celebration Crate:

In the heart of this land, where warlords tread,
Seek the seat where destinies are read.
Above the halls, where banners wave,
Sits the treasure that you crave.

Go to Maldraxxus at 50.00, 73.80, above the Seat of the Primus. The crate is in the statue, right below the ribcage, near a portal to the inside, not on top of the entire structure.

/way #1536 50.00, 73.80 Inside statue, beneath ribcage, to the right of portal.