To get the health potion trophy as fast as possible, destroy all of the containers in the first area you load into, then after you collect everything, menu and start a new game, rinse and repeat. The trophy carries over saves, and the first area has upwards of 60 health potion drops.

To get the item trophy, you have two different options.

1. You can grind the end of Azure Cove, not destroying any portals and just grinding enemies until you get the 500 item drops
2. You can play Vulhe Castle over and over again, which is more fun yet slower, but it also has the benefit of dropping items that can be converted into stronger boosts, so it gets faster each run through.