Cattails are a great survival food

Bullrushes_cattails
They will have no food with them for the 30 day trip. They will need to find everything they will eat. There are many eatable plants in the bush like Cattails which contain the nutrients they will need to keep up their energy.
In addition to the rhizomes, cattails have little known, underground, lateral stems that are quite tasty. In late Spring, the bases of the leaves, while they are young and tender, can be eaten raw or cooked.

Bullrushes_cattails
Cattails
Cattails or bulrushes are wetland plants, typically 1 to 7 m tall ( T. minima is smaller: 0.5-1 m ) , with spongy, strap-like leaves and starchy, creeping stems ( rhizomes ) . The leaves are alternate and mostly basal to a simple, jointless stem that eventually bears the flowers. The rhizomes spread horizontally beneath the surface of muddy ground to start new upright growth, and the spread of cattails is an important part of the process of open water bodies being converted to vegetated marshland and eventually dry land.
Check out the survival facts on how they intend to go about it.