So, mostly this will depend on the location of the Vikings that you are looking cosplay as. The Vikings spoke the North Germanic language of Old Norse. This was split into two main dialects, Old West Norse and Old East Norse. West Norse would have included places such as Norway and Iceland. On the other hand, East Norse would have been spoken in places such as Sweden and Denmark. Old Norse would then grow into modern Icelandic, Danish, Swedish, and Norwegian.^1

In Denmark agriculture was of great importance. Typical farm products included barley, rye, oats, peas, cabbage, and beans. They also used, goats and sheep for milk and meat and poultry for eggs and meat.^2 This was further supplemented by mussels, hunting, and scavenged fruits, berries, and nuts.^3 Fishing was practiced on the Danish coasts and lakes, but was not a large part of the Danish livelihood. Whereas Sweden and Norway had a much lesser focus on agricultural production. While it was still important, the limitation of the landscape pushed more of a focus on animal husbandry, fishing, and hunting depending on the local conditions. Typically, they raised sheep, pigs, and cattle. Some of the animals the Vikings hunted in these places were reindeer, elk, seals, walruses, whales, as well as, other birds and animals.^2 The specific animals did vary depending on local conditions. Not much is known about the specific dishes. Raw food has been found at archaeological sites, but what was actually combined is still for the most part unknown.^3

The Icelanders were a bit different when it came to food. Due to its cold interior, much of the center of the island was uninhabitable. There was a lack of predators which made it ideal for raising livestock. However, cattle was not as prominent as sheep raising. The raising of goats and pigs was largely discontinued after 1000. Farming, fishing, and hunter-gathering were also present on the island. They gathered birds eggs and beached whales and hunted seals and birds. Later sources note that often the milk would be curdled by rennet to create a higher protein version called skyr. It would be something close to yogurt. In addition, meat was often smoked or boiled. Boiled was more common because then it could be placed in súrr to preserve it. It was essentially sour whey and would give the meat a sour taste to it as well.^4

The Vikings carried a range of weaponry during the Viking Age. Swords took prominence in Southern and Western Scandinavia. Along with the sword, the battle-ax was quite popular in Western Scandinavia. On the other hand, the spear was more prominent in the east. Ibn Miskawayah mentioned a Viking described in the Caucuses, who used primarily a spear and shield, but also had a sword, ax, and dagger-like weapon. The dagger-like weapon appears to be referring to the fighting knife which has been found in Viking graves around the Baltic. Spears and bows typically were used both for hunting and warfare. However, the bow was later replaced by the crossbow in warfare. Shields were typically wooden, round, and a meter in diameter. Many had a boss made of iron in the middle of the shield behind which the grip would lie. The front of the shields would either be covered in leather or painted.^5

As for armor, the Vikings would more commonly wear leather jerkins and caps. They did wear metal-mounted helmets and chainmail as well, but those are not as well preserved in graves.^5 In regards to footwear, the Vikings would have worn shoes, ankle-boots, or taller boots, that were fastened by a strap. These would have typically been made of goat skin. Clothes themselves were typically made of woven wool or linen. However, linen was used to a much lesser extent than wool. Fur was also used to trim clothes or made into cloaks. Clothes could also be decorated with appliqué, embroidery, or metal-wire. Garments were often dyed as well.^2

With clothing it is important to remember that it is not too well known what the poorer classes would have worn. Most of the burials that have been found are of the upper classes and that is where the most knowledge of Viking dress lies. Men have been found to wear plus-fours (tied below the knee), ankle-length trousers, or mid-calf trousers. For a shirt, they often wore a shirt or tunic could be tight or loose and worn over an undershirt with a belt.^2 In addition to this shirt, they would wear a cloak made of a heavier material and fastened by a ring brooch or by strong ties over the right shoulder.^6 On the other hand, women would wear an over dress that reached from armpit to mid-calf/lower with a straight cut on the bottom. There were two long straps in the back and two short in the front that were fastened by two oval brooches in the front on the shoulder. Sometimes a chain could be hung between the two ovals and sometimes even a trinket from that chain.^2 A long shift would then be worn under the dress. It was typically loose-fitting with either short or long sleeves and a split-opening at the neck.^6 This, however, was the fancier costume. The more standard garment was a long dress that fit tightly. A shawl or cloak fastened by a brooch in the front could be worn with the dress.^2

Sources:

1. Viking Language 1 by Jesse Byock

2. The Vikings by Else Roesdahl

3. "Resources and Settlements" by Peter Sawyer in From Viking to Crusader: The Scandinavians and Europe 800-1200 ed. by Else Roesdahl and David M. Wilson

4. Viking Age Iceland by Jesse Byock

5. "Weapons and Their Use" by Pirkko-Liisa Lehtosalo-Hilander in From Viking to Crusader: The Scandinavians and Europe 800-1200 ed. by Else Roesdahl and David M. Wilson

6. "Dress" by Sigrid H. H. Kaland in From Viking to Crusader: The Scandinavians and Europe 800-1200 ed. by Else Roesdahl and David M. Wilson