OK, here’s a neat take on building a kayak… using 2" (or 1") EPS (expanded polystyrene) foam panels. Layer them like a cake and glue together, carved to shape. The builder calls it the Sawfish, and it looks like a fine craft.
And one that most anybody could build with minimal tools and space.
I do note that (like me), he finds that getting the supplies he wants is difficult. The standard local stores never seem to carry quite what you need (in his case 2" EPS foam), at least without buying a pallet of it.