In Harry Potter and Deathly Hallows, Hermione had everything packed except for food; she had clothes, money and books. But she didn't have canned food.
Inside of the book they were practically starving when they were on the run, she had earlier put a extension charm on her bag, so what was stopping her from adding canned food to the bag? All they had to eat was what they scavenged, like fish and mushrooms and a few things she bought from the store.
Hermione thinks of everything why didn't she pack food? And don't say she didn't have enough time she could have got it when she was getting the money from her account or when she bought the food from the store when they were on the run or even when they were in Grimauld place?