Easiest access to the “inert gas” piece is dry ice from your local grocery store. CO2 is heavier than air. Wrap some in a tea towel and put it in the bottom of the bucket before adding the food. Then place the lid on but do not close. Keep in a place without significant air movement while the dry ice sublimates, pushing out the lighter gasses, before sealing the lid. This takes a few hours.
Times and amounts are purposely vague, as I don’t remember them, but it should be easy to look up. If not, err on the side of too much and too long - the extra gas will just seep out the top.
A lot of good advice on this thread, particularly the emphasis on social connections and food. Given OP asked to assume near or total economic collapse though:
Some people advocated building up money savings. If you are convinced there will be runaway inflation (part of what I assume is meant by collapse) then this is exactly wrong. The thing to do would be to convert as much money as possible into durable goods while the money still has any value. Look into the history of prior examples like the collapse of the deutsche mark in 1922, and the rush on payday to buy necessities immediately.
Gold is also being suggested. If your threat model includes social collapse gold won’t do you much good. Gold has financial value but no use value for individuals (it is useful industrially, but not in a way you can take advantage of). Unless you’re planning to run, bulkier but more immediately useful goods like food and tools are likely to hold more value. When everyone’s starving, a baseball bat to guard it with is worth more than a lump of shiny but useless metal.
If you aren’t assuming social collapse, foreign currency is another option. Be careful, because you want to pick one that is not likely to track your local currency and fall together. The advantage here is that when your local currency stabilizes, the value of gold will drop quickly and it will be very hard to guess exactly the right time to cash out. Foreign currencies won’t have that same crash effect.
All that said, don’t jump into action out of panic. Take time to think it through calmly - collapse is probably not coming in the next week or two. The actions that will save you financially in a collapse can destroy you if that collapse doesn’t come. Make a plan for what to do if you’re wrong to avoid shooting yourself in the foot (or, as many people do after that kind of mistake, the head).