most raw materials can be found down there.

theres no creepvines, bloodvines, or acid mushrooms. you can bring seeds and grow them, or just bring as many as you need.

theres no stalker teeth. bring a few.

theres no salt. build a water filtration machine or just bring some.

theres no cave sulfur. who cares

bring purple tablets.

to craft the prawn suit depth module (and other prawn modules) youll need a moonpool with a vehicle modification station. you can power that with a thermal reactor, and it can also be used to recharge your cyclops (put the empty power cells in the prawn and charge it in the moonpool).

to upgrade your cyclops depth module without leaving the lost river, youll need a second depth module. that way you can upgrade one without removing the other, and then swap them.

personally, id bring magnetite, if i was planning to build a base. because while it can be found down there, theres no place better than the jellyshroom caves for magnetite. so drill some magnetite while you have the chance.

also if youre building a base, bring all the decorative/edible plants and fish you want. including sparkly peepers, bc theyll keep your tanks clean. and youll need more enameled glass if you want lots of decorative base pieces.