The setting is extremely cold all the time, and traveling around takes days. How would travelers bring water rations with them and keep it from freezing? There are almost no un-frozen bodies of water readily available, and I'm not sure if its realistic to have them melt down snow at camp each night. Or how they would use the water they boiled the next day, without making camp and boiling more water multiple times a day.
I'm not sure if its realistic to have them melt down snow at camp each night
You should consider that if they cannot light a fire when they camp at night then there's a reasonable chance that they might not live until the morning. Arctic nights are cold, and medieval insulation was either poor, or quite heavy. People who lived in the arctic would of course be suitably equipped and well practised in this sort of survival, and show that it is possible, but this isn't a skill that can be easily communicated to just any traveller at short notice.
Inuit hunters would have consumed some of their prey raw, on the spot, including the blood... with mammalian prey, this is an effective way to stay warm as well as nourished and hydrated. They only cooked food when they'd been on the move for a day, but note that this implies that they carried suitable equipment to actually cook things (such as blubber-fuelled lamps).
How would travelers bring water rations with them and keep it from freezing?
Note that it is possible to eat frozen meat, and the peoples of the arctic circle do just that. Not only will this help the meat to last longer, but if it was uncooked before freezing then it can contain additional nutrients not present in aged or cooked meat that are otherwise hard to come by in arctic winters, such as carbohydrates from intramuscular glycogen.
Clearly it would be possible to keep some food and drink within the warm layers of the travellers clothing, though this would be a limited amount. If pack animals were available, such as caribou/reindeer, it could be possible to make use of their body heat to keep a larger amount of food and water thawed, though obviously that needs to be counterbalanced by the calorific and water demands of those animals.
I would say the best way to keep water from freezing is to keep it close to the body of the bearer.
Flasks were usually made with the stomachs of lambs or other animals, so they were quite flexible. They could be stored inside the clothing, so to be both better insulated from the outside and also closer to the only readily available heat source.
Replenishing them would require melting ice or snow whenever a fire is lit, but I guess the Arctic doesn't lack them.