We don't have synonyms for back pack yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are backpack, back talk and backtrack.
°A knapsack, sometimes mounted on a light frame, but always supported by straps, worn on a person's back for the purpose of carrying things, especially when hiking, or on a student's back when carrying books.
°A knapsack, sometimes mounted on a light frame, but always supported by straps, worn on a person's back for the purpose of carrying things, especially when hiking, or on a student's back when carrying books.