Real trading

Instead make exchange between item, consider to be able to sell (earn Money) or buy (spend money) with all items available in our island. That's really more real.

Money are not that usable in small communities, especially if resources are scarce. For them to work theirs value would have to be secured somehow. Barter is usuall in such cases, especially in post-apocalypse situations (you cannot eat money, or at least it is not recommended).
Trading system could be more flexible, but all those trades were made for some level of balance. Otherwise you could be changing anything into anything, making it too trivial.