Just some suggestion/Idea from a player whom yet to play.

1) Individual inventory space.
1 bag for each class of items [Resources/ materials, food, tools, equipment (or to be equipped)], when Raw food is full while the rest isn't you wont be able to carry anymore raw food, but you still can carry more non-raw food-related.

*bag size up-gradable. (for each classification)

2) Equipment slots.
Let us equip our equipment! (not put it in bag for item to take effect), along with new equipment's like diving suit/ helmet? (which will further increase our tolerable water pressure)
Not jumping off the sub at 250+ depth with default gears and

3) Renewable resources. (by natural or man-made)
Implement a method to obtain renewable resources. For example: like a replicator machine (need to analyze material first) which is able to duplicate materials a list of materials, that requires a huge amount of power, maybe 10~12 solar to one? (Slowly...)

4) Cook-able/ edible predator meat.
^as says, Cook & Eat those 'Stalkers!'. Able to put the whole 'Stalker' into inventory (raw food compartment if has space, example: 3 x 6 -ish size)

5) Oxygen Leakage.
Bitten by predator etc or any sharp (with sharp teeth) will/or might puncture a hole in the suit/ oxygen tank will cause an oxygen leakage. (oxygen drain faster depend on size of hole)

6) Bleeding under water/ Combat Wounds.
Bleeding while under water with or w/o an oxygen leakage will cause/attract/aggro surrounding predator(S) toward the player or target (which bleeds). Use bandage in base to fix wound.

7) Deadly Predators (when blood is in the water)
Predators which will attack non-stop till target is dead. which flesh wound will further aggro/attract more surrounding predators. Hence the loop.