We don't have synonyms for packsack yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are backpack, rucksack and ack-ack.
(n) :
(chiefly US) A backpack, knapsack, rucksack or similar bag packed with provisions or personal items, especially as carried by a traveller or a hiker, and often slung over the shoulder.
(n) :
(chiefly US) A backpack, knapsack, rucksack or similar bag packed with provisions or personal items, especially as carried by a traveller or a hiker, and often slung over the shoulder.