So first of, I love the new belt feature. It was much needed. While digging through your inventory while beset by zombies was stressful and scary, often it wasn't really immersive or engaging, and more often frustrating. This is something, however, that I feel could be expanded upon to deliver some higher overall quality of life for players without greatly affecting the code base or decreasing the difficulty.
The strongest example of this is cigarettes. Currently you have to dig through your inventory to smoke a cigarette, though any smoker keeps a pack on hand. Adding a non-essential pocket button, and binding it to a key, let's say 6, would give your character the ability to smoke when they start feeling antsy if you put a pack in that pocket.
I think 2-3 of these slots would be reasonable, and binding specific items to these slots could help with various quality of life actions that aren't actually that difficult for a Player Character to do, but are frustrating for a Player themselves to access through the menu system. Below I will list some possible items and their benefits in pocket slots.
Cigarettes: Easily smoked to help manage anxiety, useful for RP
Wrist Watch: Silence an alarm at the press of a button, since it is only on your wrist anyway
Walkman: While it currently does nothing, putting it in a pocket with headphones will give you access to a music happiness buff at expense of your characters hearing
Flask: While liquor bottles themselves are too large to fit in pockets, if a flask is added then characters will have access to a way to drink out on the field, while providing ample opportunity for RP
Notebooks/Maps: A player that likes to use these features, for RP or otherwise, will be able to make more use of them with the feature being available at the click of a button
Snacks: You aren't going to fit a whole ham in the pocket, but perhaps you could prepare a ham sandwich for lunch while you are out scavenging. This would encourage using the cooking skill to it's fullest rather than being ignored by many players
Tissues/Handkerchief: Have a cold? Pull a tissue from your pocket to stifle some sneezes
Sand: POCKET SAND!!!! (jkjk)
These are all the ideas I personally have on the matter, thought up while writing this. This originally started simply as a smoker button idea, but evolved while explaining it. Please, if anyone else has ideas, please post them. I would like to see this feature implemented.