Such as vikings or hunters who would go on adventures often. I roughly know from doing some research backpacks as we know them are a relatively modern item from around the 1900's. Before that from around 1700 onward they used packs with a single shoulder sling like a female purse is today. But what about from the 5th-10th century? Did they just not carry anything around with them on small expeditions?
An illustrative example from my area of interest is the Roman Army who (to put it mildly) did a lot of walking and needed to transport a fair amount of equipment. In the earlier republican period soldiers had most of their equipment carried by animals in the army's baggage train. This makes sense as, in the ancient world, animals were used to carry most things over land, either as muscle power pulling a cart or directly in bags tied to the animals backs.
The baggage train never entirely went away, but following military reforms in the late second century BCE, legionary soldiers began carrying more of their own equipment. They carried it in a satchel/pack (called a sarcina) tied to the end of a pole (called a furca) that they carried over their shoulder (similar to, but not exactly like, a modern bindle). You can see legionaries with sarcinae on Trajan's column (e.g. the poles with packs and pans hanging from them on the left side of this image): http://www.trajans-column.org/wp-content/flagallery/scenes1-5/img_2025-web.jpg
For much more info on travel and baggage in the ancient world, I recommend Lionel Casson's "Travel in the Ancient World." It's older but still quite good and very readable for a general audience.
As for the Vikings, they definitely had backpacks, and we have extant remains.
Remains of a Gokstad backpack: https://1.bp.blogspot.com/-SqF_xn-apBo/V6d3N80t72I/AAAAAAAADXs/ObH-tEEhxiczI2bt3lRjdcTipHTgszrAQCLcB/s1600/VSM2Backpack.jpg
closeup picture:
possible reconstruction, how it looked like:
https://i.pinimg.com/originals/a9/ff/4f/a9ff4fa8f990506920abf96061437b75.jpg
The backpack was made of two thin boards, that made the top and the bottom of a basket-like, stiff backpack, worn on two suspender belts.
Aside from backpacks, Vikings and related peoples of the Middle Ages used bags too, handles of which are common find in archaeological investigantion of Viking settlements.
various types of wooden handles:
https://nattmal.files.wordpress.com/2015/07/haithabu-bag.jpg?w=380&h=251
possible reconstruction, or how the bag looked like:
https://i.pinimg.com/736x/0a/7f/a2/0a7fa2b6fb07177b9f834c38a1a76677--viking-age-the-vikings.jpg
Other than that, equipment could have been carried in sacks, or wrapped up and tied to a wooden frame.
One of the oldest finds of backpacks in Europe is the Otzi's backpack from the as early as 3400 - 3100 BCE.
There is no reason to believe that such a simple design would vanish since then.
https://i.pinimg.com/736x/0a/38/41/0a38414fc9413a9f5464f8000c962737.jpg
