Was already suggested like 20 Times in the comments.
And its in the description of the mod under "Possible Features in the Future:".
I will work on this feature when i think the mod is bug free enough.

I have to admit, i didnt see this in the description, nor have i seen a response to the suggestion in the comments, therefore i wanted to make sure it reaches you.

Thanks for your response :)

No problem and i can assure you i will read every comment.

@ [Phönix] Xaneas I just want to say great job on the mod you made! Better inventory maybe one of the best mods I've seen. I run a private server and I have to make a better inventory for my players because they are much older and can't use the A3 default easily. After seeing your "Better Inventory Mod" I would like to use this as my base with the 3 list box idea. My inventory system must have custom buttons made just for my server so I can't use your mod for this reason. My custom version would not work with any other servers so you would never have to worry about it being uploaded as a public download. I would however like to give you credit as to the idea of my inventory system and because I stream if any viewers seen my inventory system and wanted it I would send them to your mod the "Better Inventory". I really hope you agree and like this idea, but I understand if you do not. Also the reason I posted this here is some of my custom buttons will include buttons like the requested one above and I would be happy to share stuff like that so you can add them to your mod when I have them working. Again you have made a great mod here keep up the good work! :)

I finally checked out this mod, and it's fantastic.
Works seamlessly with everything else I have loaded and I'm currently using an SQF for item stack moving.
It's called "Moving Stacks" by Andrea & EliteWarrior142. It was on the Armaholic site but I haven't seen it anywhere else since. I have a zip file of it saved and I've posted it on the Wasteland Walkers discord.