Lore
Old and used backpack was added into the game on the version 7.5 and it is an old backpack used by Sam on the old days where he was an explorer. Once, while he was exploring Ulderek's rock (also known as the orc fortress), he got raided by some orcs and lost his backpack when he fleed. If you return his backpack to him, he'll present you with the finest armor made by the famous blacksmith race: a dwarven armor
How to get the old and used backpack
The backpack can be looted from an orc (regular type) that rarely respawn on orc fortress. Although there are lots of regular orcs in the fortress, the point where this specific orc spawns usually have only other types of orcs, such as berserk, warrior and riders, so if you spot a single orc in the midst of the others, you'll know you found the correct orc.
You can find this specific orc in the northeast tower of the fortress, just as shown on this image here:
Helpful information for those who want to check the orc
While CipSoft itself doesn't give any timer or method to check if it is still alive or not (its kill statistics just get mixed with common orcs), data got along the years made specialists infer that the medium resp-time is about 2 weeks (13~16 days), so if, by chance, you know the date that someone got it the last time, you can program yourself. Another common method is to put a level 40~50 on the resp and log in sometimes just to check, since you can logout nearby and won't be bothered by any creature that could kill you.
Another useful intel is that, even though it is considered a common creature, it does not drop 2 backpack's neither on double loot events or with activated prey system (though this information is not 100% sure).
After getting the backpack, what can I do with it?
After you get the backpack, you can either use it as a normal container (it's a red backpack with the following message when you look into it: You see an old and used backpack (Vol:20). Imbuements: (Empty Slot). It weighs 18.00 oz. A label on the backpack reads: Property of Sam, Thais.) or procceed with the quest.
If you want to continue the quest, go to Sam and tell him about his backpack. After retrieving it to him, you'll receive an achievement (Backpack tourist) and he will send you to Kroox, in Kazordoon, to get your dwarven armor (if you don't care for the achievement, it would be interesting to sell the backpack, since its value is way higher than dwarven armor's itself).
Now go to Kazordoon and talk to Kroox. He'll tell you that he doesn't have a dwarven armor with him but you can take one from their storage. You'll receive now permission to enter the quest door south of the hole leading to the floor of Crusader's helmet quest. Just go there and open the chest to retrieve your dwarven armor.
You can check the whole quest spoiler here