Both Uses of

forage
in
Main Street, by Sinclair Lewis

In its solid rooms Carol and Kennicott found prints from other days which the house had seen—tail-coats of robin's-egg blue, clumsy Red River carts laden with luxurious furs, whiskered Union soldiers in slant forage caps and rattling sabers.†
Chpt 2 *

forage = search for and gather -- often food and provisions

She felt old and detached through high-school commencement week, which is the fete of youth in Gopher Prairie; through baccalaureate sermon, senior Parade, junior entertainment, commencement address by an Iowa clergyman who asserted that he believed in the virtue of virtuousness, and the procession of Decoration Day, when the few Civil War veterans followed Champ Perry, in his rusty forage-cap, along the spring-powdered road to the cemetery.†
Chpt 18

Definitions:

(1) (forage)
to search for and gather -- often food and provisions
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

More rarely: Forage can imply taking other's food or supplies as when soldiers forage on nearby farms. As a noun, it can reference the items found. Finally, at times (especially in classic literature) it is used in reference plant material eaten by animals.