Loot can be identified as the items that are in the small bags spread throughout the maps and dungeons. They are also shiny objects that you see along some walls and in some trees. When you pick up loot, it will be a white bag if it's a bag and a blue bag if it's a shiny object. There are multiple spawns in each area for loot and this trophy only counts each spot once. This means if you picked the same bag up 1,000 times, the trophy would still not unlock. It helps to run through each field and dungeon multiple times keeping an eye out for new loot spawns in order to reach the 800 necessary for this trophy. Milla has access to a couple areas unique to herself, therefore it's slightly easier to get this during her playthrough. It's worth noting that you CANNOT carry this progress over to a New Game+, so plan on doing it in one playthrough.