Here are two Video guides to all the collectable in the game. Hope this helps. I do not take any credit for these videos. If any negative votes please leave a comment. Thank you
Edit 7/19: Thanks to juicyluce9: To get the collectibles by the tank in the battle of Somme, all of your platoon must be alive (there's an achievement for this) and you must talk to them (press A) and a heart will appear in a speech bubble over their head (guy at front and guy at the back) and then they'll drop the collectibles for you to pick up
Update/Suggestion by Lockyz75 : Just thought I would mention, I had all collectables but achievement tracking said 99% . My console was set to instant start up and last couple of achievent had unlocked but the message didnt come. I have had this a few times now, but it returns to normal when switching to energy saving mode. I did this and restarted the console and the achievement was unlocked. So this might work for other people too.
Update/Suggestion by Apache117X : If you don’t want to watch a video this site has them in text. Link https://www.gamesradar.com/valiant-hearts-great-war-historic...