Modpack is FTB Infinity Evolved 2.3.3 with expert mode active.
I play the game with server instance on the same PC as the MC client. I use the serverstart.bat script.

Setup:
Cache (any except the highest tier) with contents (any item) is placed in the crafting grid with upgrade materials.
Enough upgrade materials and extra caches to upgrade at least one additional cache are placed in the inventory of the Project Bench.
Shift + LMB on the crafting result will craft the desired upgraded caches. All caches that are crafted/upgraded will have the contents of the first cache (the one placed in the crafting grid in step 1).
The duped items are fully usable. If the additional caches already have contents, they will be overwritten with the contents of the first cache.

This works with previously placed caches as well as newly crafted ones.

When hovering over the crafting result I noticed that you can view the resulting caches contents.