Oxygen Tanks
I used the tanks pictured as my reference. But they are 53 kg. Firefighters wear SCBA units that typically weigh under 5 kg. They usually last only 75 minutes at most.
However, according to the specs on the website below, these 50 L tanks would hold 10 cubic meters of O2, and a person at rest would use 550 L (or 0.55 cubic meters) in a day. You would have to use a rebreather mask to reuse your exhaled oxygen. In that case, it would be reasonable for the tanks in my story to be 4 L tanks or smaller and last a little more than a day.
But since this is set in the future, there might be tanks that hold a day’s worth of oxygen in a tank similar in size and weight to our 4 L tanks that would not require the use of a rebreathing mask.