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You can make temporary paper glue out of flour and waterNot useful for sealing submerged parts of a shiny metal structure though.
>Either you have enough money to buy some glue, or you can spend time teaching your kids how to make it.
This is how it seems to go. However practically you need grain, so you need a trip to a field with grain in, which would be a bus ride, which would cost more than walking to the shops to buy glue.
Once you're at the field (assuming you have permission), you'll need to gather the grain. Scythe? Sacks? I know from experience that you get little flour from the grain you can hand collect and grind with a couple of flat stones in a couple of hours. Were talking young kids here too, getting them to gather grain won't be much fun when they're moaning "I thought we were making junk boats ... can't we make our boats".
I'm not trying to be completely obstructive (honest!) - making our own epoxy sounds more fun (but again, hidden costs) - but perhaps these things will come later.
That is kind of what I meant by hidden costs.
To recapitulate often one doesn't realise the benefit of the resources one has available. Making a piece of furniture for example someone will say "use your drill press", "use a nail gun", "use an orbital sander", etc.: obviously once one has these things the usage cost is near zero but the acquisition cost is high. These acquisition costs get hidden.