In Junior High or High School (I can’t remember which) my science teacher showed us that if you slightly wet a biodegradable packing peanut you can stick them together (actually I think he ate one in class but I’m not going to recommend that here). That’s stuck with me this whole time and I can never help but stick a few together when they come in a shipping box.
The biodegradable packing peanuts are made from things like grain sorghum or cornstarch. They are lighter and more airy than the traditional polystyrene type. The best part about them though is with just a bit of water they stick together.
You only need a small amount (to much and they’ll basically disintegrate into a gooey mess (though that’s fun too).
The odd shape of the peanuts makes for some unconventional shapes but it’s still fun to see what you can come up with!