When you create a new game the random seed gets reset so you'll get entirely different items but they'll remain constant throughout the play-through.
Well, this is not really true
Changing the seed will change the RNG output (obviously), however using the same seed for two games still won't guarantee the same loot.
The seed is only used for initialization (so you'll get the same random number in the two games at the very beginning of the game), however each subsequent generation changes the internal state of the generator, so depending on the players actions the RNG states will be completely different in the two games, despite the same seed --> different loot.
Incidentally, this is the reason why saving the seed is not a reasonable approach to prevent save scumming. As many events (eg. NPC wander behavior) are tied to the RNG, simply waiting a few seconds more after reloading a savegame will change its state sufficiently enough to give you different loot.
