I think this is a great idea, and intend to participate, in whatever way I can.

This feels like another good candidate of adding to the rationalist/secular calendar of holidays.  These only get invented when people decide to try new things, so I doubly appreciate this.

As for what to do, a simple thing I would be interested in is just learning more about the story.  Who were they, how did they get to be at the seedbank?  What was the onset of the siege like, and how did they adapt as things changes?

I'd also be learning about other seedbanks, and how they came about.

Finally, as a more ritual-y thing to do, maybe we could make a little seed bank of our own.  I expect it to mostly be symbolic.

uncomfortable squirm

In my culture, one is to be super wary of lionizing martyrs.

I want to be excited about cool new holiday ideas. I think trying a fast in a coordinated group is a splendid idea. I want to celebrate the amazing capacity of humans to care about others and to do hard things for good reasons.

but pain is not the unit of effort.

dying for the cause is not a success.

not every cost is avoidable, but i never, ever want to become the kind of person

who mistakes the price sacrificed for a value bought

In my culture there's a meta-tradition around ritual hardships or labors: you are to set aside at least 5 minutes, by the very clock, for considering how you might cheat. If you find you could get results without the hardship, you are expected to cheat for the results and then go find some other way to challenge yourself.

A bit of advice from my own experience with fasting.

Hunger is strongest roughly between hours 6 and 12 after you stop eating. There's some variation here, but my vague understanding is this has to do with something about blood sugar and insulin response cycles.

Generally once I make it to 12 hours the rest is smooth sailing, at least in so far as hunger becomes a background annoyance rather than a strong urge.

At around 20 hours or so I find mental changes start to happen due to what I presume is low blood sugar. It's nothing insurmountable, just something like mental fuzziness that makes it hard to do mental activities at the limit of my ability.

I'm not sure what happens past 24 hours; never gone longer than that.

I'll offer up my own fasting advice as well:

I (and the couple of people I know who have also experimented with fasting) have found it to be a highly trainable skill. Doing a raw 36-hour fast after never having fasted before may be miserable; but doing the same fast after two weeks of 16-8 intermittent fasting will probably be no big deal.

Before I started intermittent fasting, I'd done a few 30-hour fasts, and all of them got very difficult towards the end. I would get headaches, feel very fatigued, and not really be able to function from hours 22-30. When I started IF, the first week was quite tough. I'd have similar symptoms as the fasting window was ending: headaches, trouble focusing. But then right around the two week mark, things changed. The symptoms went away, and the hunger became a much more "passive" feeling. Rather than hunger directly causing discomfort, the hunger now feels more like a "notification". Just my body saying "hey, just so you know, we haven't eaten for a while", rather than it saying "you're going to die if you don't eat right this moment". This change has been persistent, even during periods where I've stopped IF.

Both of the two others I've seen try IF have reported something similar, that the first few weeks are tough, but then the character of hunger itself starts to change. Today, I can go 24 hours without eating fairly trivially, ie without much distraction or performance decreases from hunger.

Going 36 will still be a challenge, but some pre-training may make it easier! Of course you may be specifically trying to test your willpower, in which case making it easier may be counter productive. Either way, this seems like a cool idea for a secular holiday. Best of luck! 

This sounds like a good (and somewhat productive) way to celebrate.

I'll start an attempt to as well, if my parents don't object too much (I'm currently 17 and still live with them).

I've never fasted any longer than 16 hours before, so I'll assume this will be hard... Does anybody have advice on how to make the 36 hours go over a bit easier?

I propose we surround ourselves in edible seeds, too. 

Any thoughts about supporting biodiversity (perhaps especially for food crops)?

Great idea! I have marked my calendar. 

I think this is a really cool idea. Good luck with your fast.

At the risk of undermining your post by second guessing the decisions of people made 80 years ago under duress, I can't read that article without thinking "If they were needed there, alive, to guard the seeds, maybe they should have eaten some of the 370,000 seeds?"  To be clear, that does not diminish my respect for their restraint (I certainly could not have done that) or Vavilov's contributions.

Just wanted to say that I think most rationalist "holidays" or "rituals" are pretty cringe, but this one strikes me as something much more real and valuable. I'm not sure I agree with your concept of "Patron Saint holidays" for the community as a whole but this one seems at least somewhat virtuous and noble in a way that I think a lot of other stuff misses.