The video below shows unmarked chests locations in White Orchard. If you’re still playing within the map or decide to play the game a second time (or through the new game plus mode) and start over from the beginning, discovering these chests locations will surely be beneficial as you can obtain a some coins, crafting mats and some recipes from the chests.
Video credit to NaylaGames
The 3 chests on the middle river is fairly close to each other so you can just swim straight to them as shown in the pic below.
In the windmill area, don’t forget to check the cabin. When you enter it, turn right and look below to reveal an entrance to the basement which contains several chests.
One of the chests here requires a key. The key can be obtained from a dead body located before the bridge as shown in the pic below.
If you are interested to find hidden/unmarked chests in Velen and Novigrad, see this post.