There are a total of 121 supply boxes you will need to get among the 6 open combat missions. You will also want to grab plate carrier upgrades and armaments to also grab these:
The following videos will take you through all the items in the open combat missions:
0:00 - Silenced WSP Swarm & MTZ-556
0:34 - Heartbeat Sensor & Mosquito Drone
0:52 - Silenced Expedite 12 & Mosquito Drone
1:14 - PILA
1:39 - 556 Icarus & Snapshot Pulse
1:58 - Explosive Victus XMR
2:27 - Munitions Box and Cruise Missile
3:03 - RPK
3:28 - Pulemyot 762, Ascender, and Parachute
3:40 - Armor Upgrade 1
3:48 - Silenced ISO Hemlock
4:19 - UAV
4:41 - Signal 50
5:05 - Hybrid STB 556
5:23 - Incendiary Bryson 800 &UAV
5:58 - RGL-80 & Sentry Gun
6:16 - KVD Enforcer & Bomb Drone
6:34 - Armor Upgrade 2
6:44 - BAS-B
7:13 - GS Magna
7:26 - Recon Drone
7:46 - Silenced Rival-9 & Bomb Drone
0:00 - Silenced Holger 556 & Sentry
0:40 - Incendiary MCW & Stealth Bomb
1:10 - Sidewinder & Sentry Gun
1:56 - UAV
2:10 - Bomb Drone
2:28 - Basilisk & SAM Turret
2:55 - Hybrid STB 556
3:16 - PILA
3:24 - Anti-Armor Rounds
3:45 - Incendiary MTZ Interceptor
4:01 - Explosive Crossbow
4:40 - Signal 50
4:58 - Silenced Lachmann Sub & Incendiary Bryson 800
5:36 - Precision Airstrike
5:57 - Fennec 45
6:12 - Cronen Squall & Holger 26
6:28 - Carrier Armor Upgrade 1
6:50 - Silenced VEL 46 & Armor Box (Bomb Drone & Sentry Gun)
7:23 - Incendiary Haymaker & HCR 56 & Munitions Box & UAV
8:15 - Heartbeat Sensor & Silenced Expedite 12
8:47 - Incendiary FJX Imperium
9:12 - Silenced Cor-45 & Optional Carrier Armor Upgrade & RGL-80
9:46 - Incendiary Sakin MG38 & Mortar Strike & Carrier Armor Upgrade 2
10:34 - KV Inhibitor
11:03 - VTOL
11:20 - Minigun & Snapshot Pulse
0:00 - Silenced Victus XMR
0:28 - Kastov 762
0:45 - Plate Carrier Upgrade 1
0:58 - Heartbeat Sensor
1:10 - Silenced Crossbow
1:21 - Incendiary RAAL MG & Bomb Drone
1:53 - Incendiary Lockwood 680
2:03 - Plate Carrier Upgrade 2
2:15 - Armor Box
2:30 - Silenced M4 & Sentry Gun
2:52 - Silenced SA-B 50 & Cluster Mine
3:20 - Munitions Box
0:00 - MCW 6.8
0:38 - STB 556
0:48 - Carrier Armor Upgrade 1 & Cruise Missile
1:08 - Incendiary Bryson 800 & Recon Drone
1:26 - Silenced M16
1:42 - Heartbeat Sensor & Night Vision Goggles
2:01 - Ascender
2:18 - Explosive Katt-AMR
3:25 - Silenced DM56
3:44 - Cronen Squall & Bomb Drone
3:58 - RGL-80
4:13 - Anti-Armor Rounds
4:29 - Pulemyot 762
4:40 - Silenced Bryson 800 & Carrier Armor Upgrade 2 & Cluster Mine
5:05 - UAV
5:23 - Minigun & Precision Airstrike & SAM Turret
5:46 - Armor Box
5:57 - Hybrid Kastov 545
6:06 - Akimbo .50 GS
6:25 - Silenced WSP-9
6:39 - Snapshot Pulse
6:54 - Silenced M4
7:08 - Explosive Crossbow
0:00 - Nightvision Goggles
0:25 - Silenced TAQ-M
0:45 - Snapshot Pulse
1:08 - Silenced COR-45 & .50 GS
1:27 - Carrier Plate Armor Upgrade 1
1:58 - Explosive Crossbow
2:27 - Silenced Expedite 12 & Incendiary MCW
2:51 - Minigun
3:27 - Silenced Kastov 762
4:01 - Silenced MTZ Interceptor & Carrier Plate Armor Upgrade 2
4:45 - VEL 46
5:08 - Silenced Striker 9 & LA-B 330
5:50 - Ascender
6:19 - RPK
7:00 - Incendiary Bryson 800
7:33 - WSP Stinger
7:55 - PDSW 528
8:13 - Anti-Armor Rounds & ISO Hemlock
0:00 - Fennec 45 & Mortar Strike
0:27 - MCPR-300
0:55 - Incendiary Raal MG & Ascender
1:13 - Silenced Striker & Cruise Missile
1:35 - Silenced Expedite 12 & PILA & Signal 50
2:14 - Snapshot Pulse
2:39 - Heartbeat Sensor & Silenced 556 Icarus
3:18 - Silenced Rival-9 & Armor Carrier Plate Upgrade 1
3:54 - Anti-Armor Rounds & Cluster Mine
4:13 - KVD Enforcer & Optional Armor Carrier Plate Upgrade
4:42 - Armor Box & RGL-80 & Optional Armor Carrier Plate Upgrade
5:08 - Silenced M16 & Armor Carrier Plate Upgrade 2
5:27 - Munitions Box
5:38 - Recon Drone & Hybrid MTZ-556
5:52 - Chopper Gunner Armament
6:18 - Holger 26
6:30 - Silenced EBR-14
NOTE: If you complete all 121/121 and the achievement doesn't unlock, users have reported starting a "new campaign", and it
should unlock once you recomplete all of the supply boxes on Precious Cargo.