I agree. My great-great grandmother was confronted by foragers under circumstances almost identical to those presented in the movie. (Like Natalie Portman’s character, she was tending a baby whose father had been killed during the war.)
During the American Revolution and the Civil War, the answer is yes. Organized parties of foragers were sent out and instructed to return with food. (That is not to say all foraging was organized. There was of course the ad hoc variety as well.)
One of my Father’s first letters home from WWII asks firends to send cigarettes. 
Lee instructed his army to pay for forage in Maryland. The money was of course useless to the citizens, but it represented a sacrifice by the army.
I actually just learned today (from a Lewis and Clark re-enactor) that in the early 1800s, the US had no cavalry branch. The closest we had were dragoons, who would travel on horseback, but then fight on foot.
Would you care to elaborate? I’m not seeing how some cord on your shoulder would help you to forage. I’d always assumed they were just there for decoration.
Th efirst units of Dragoons, back in the 1600’s (in Europe) were indeed “mounted light infantry” but by the 1800’s were in practice medium cavalry. I am pretty sure the USA has always had a unit of light cav but I am willing to be shown otherwise.
The pre- (Civil) War establishment of the US Army was:
2 Regiments of Dragoons
2 Regiments of Cavalry
1 Regiment of Mounted Rifles
4 Regiments of Artillery
10 Regiments of Infantry
Totaling 13,024 officers and men.
I would like to revise and extend my previous comments about the US Army organization during the ACW.
3 Regiments to a Brigade,
3 Brigades to a Division
3 Divisions,
1 Brigade of Cavalry,
6 Artillery batteries to a Corps
This give a notional Infantry Corps a strength of 36,000 officers and men.
A six-mule wagon hauled 3,000 pounds of stuff. Each man would eat three pounds per day. In real life regiments were under-strength, so a regiment ate two wagon loads a day. If beef was provided on the hoof, it took two days for a regiments to eat a wagon load.
So a corps would eat 54 wagon loads a day (with no fresh beef). A twenty-day supply would be about six and a half million pounds. Add to that an equal amount of non-eadible supplies for 13 million pounds. Add to that 20 pounds of grain per animal per day.
(Animals of all types were at about a third per man in infantry outfits.)
Now all of this could be reduced by some foraging, or by using beef cattle, or by using foraging for (you guessed it) forage.
Also, I wish to point out that a corps’ 4,300 something wagon-loads did not imply that many wagons. Most of the stuff was laying about in supply camps, but was under the control of the corps commander.
Thank you for letting me clear that up.
Oh and in pre-war or 1812 days (and even unto the Civil war) a lot of the military might of the US was in Militia, some of it pretty good. Others- not so much.
You’d tie it around the neck of somebody’s goat or cow and lead it away, or you’d tie a bunch of jars or bags together and haul them off.