This page of the guide to Death Stranding tells you where to safely store unnecessary equipment - Sam's equipment that isn't currently needed. The game, fortunately, makes it very easy to store unused items.
Important information - don't try to get rid of unnecessary things by throwing them out of the inventory. When you move too far from them, these items will disappear from "your" world and appear in a random player's world.
You should storage items that will come in handy later (e.g. in missions where BTs appear) or those you have in excess. This can be, for example, weapons, grenades, spare exoskeletons or PCC. Equipment can be stored in Private Lockers - you will find them in every friendly location with a terminal.
When you select the option to open a Private Locker, you can move selected items from your inventory to it. Very important information - each location has a unique Private Locker meaning that their contents aren't shared between them. If you leave an item in a Private Locker in location A, you won't be able to access it from a Private Locker in location B. It is best to choose one favorite locker from each region of the map to not forget where all the spare items are stored.
The same goes for garages where you can store vehicles. For the record, garages only appear in large locations and in built shelters where there are elevators that go to the Private Room. The content of each garage is unique - a vehicle stored in one garage can't be accessed from another.
Each garage can store up to 4 vehicles. If you fill it out, visit other garages on the map to store newly purchased vehicles to them without having to get rid of the old ones.