Something like this:
This came from the backpacks suggestion (which i support), but allows more. The additional item slot (under armor) could be for backpacks. So now we'd have a way to wear backpacks in a special slot meant for them. (We don't have enough slots in my opinion.)
The mini-slots could be for items like: paramedics bag, mirrored shades, radio, ammo, drugs, lighter (the things i don't want to drop when i "drop-all").
If we had these additional slots, we could more easily drop-all and grab-all items without disrupting our intended inventory minimums. For example, we go looting for blueprints and end up getting so many other items. As things are now, we bring them back and have to sort them into different piles or containers (if we want to keep things tidy). But this takes too long and we are unable to "drop-all" because some things we need to keep with us, to go out again looting. With more slots though, we could drop-all in a single pile (for sorting later) but not lose the things we need to keep in inventory for more looting. It would be way faster.
Even Better: add a tab page so that you effectively have two inventories - the default, and the one inside of a backpack.
The above image is also taller which means more items visible vertically for slightly less scrolling.