Secronom Tower and Other Secronom Buildings
Currently there is no use to these items: Secronom Keycard, Rusty Key, and Severed Hand. The usage of these items MIGHT be similar to that of nails/planks when barricading.
The Secronom Tower is the epicenter, hence it also makes sense that the 5th Outpost (a former Secronom location) to be furthest away from the Secronom Tower. Secronom buildings will be categorized depending on their former functions; as a player advances deeper into the epicenter, the buildings encountered will be of greater former importance and risk.
The first type of Secronom buildings encountered will be deposits or shacks, for these a player will need a Rusty Key. The second type of Secronom buildings will need a Severed Hand (fingerprint detection is still functioning), these buildings will have the unique characteristic of flickering lights. The final and third type of Secronom building is also the only of it's kind, the Secronom Tower. This is NOT an "item mining" location, rather a place for maxed and experienced players to see how long they survive.
The Secronom Tower, the MOST dangerous place in the game.
The Vault
>TL;DR: Combine the Bank and the Storage.
There is no reason to have the Bank and Storage separate, as this adds to the time and the number of clicks (and pages) a player has to go through.
Request Option
>TL;DR: Allow players to request items from the Marketplace.
In the same way we are allowed to put an item in the Marketplace which another player might later exchange it for the money being asked; with the Request option, a player could put money in the Marketplace which can be exchanged for the item being asked.