If these kids were camping in an RV, or even out of a car, they could make that work, but rice requires things like a pot (heavy) and water (valuable) to make it work.
There a brief sequence early in The Blair Witch Project where the kids do some shopping.
Blair Witch Lesson 1They’re working out of backpacks, not an ice chest.
Backpack space is valuable and considering they had to fill most of theirs with camera equipment, they simply didn’t have the space to waste.