Very little to say about this one other than it will come naturally as you complete the story.
The achievement itself unlocks shortly after a cutscene (where you are requested to meet at night at a particular building).
*** Spoiler - click to reveal ***There is no boss battle between arriving at the building and the cutscene; and so no need to stock up/eat etc. beforehand despite only being a party of 3 at this point, following the departure of Nanba.