Take the coat out of the suitcase.
Take the backpack off the sofa/couch.
Sofa and couch are used in the USA.
A "backpack" is more than just a "mochila". It is large and is used for camping. A special kind of backpack is called a ruck, rucksack, or bergen.
The small pack used for books or personal items is called a "daypack" because it is used for a day hike and does not need to be big enough to carry a sleeping bag, tent, stove, etc.
Whether the mochila is big or small, for camping or books, it can be called "pack".