The box was a little longer than usual for this Things of Science unit. This because of the small balsa airplane included. This unit did come complete when I purchased it.
Someone wanting to recreate this unit can easily buy a small balsa glider or two from a hobby store or perhaps a party supply store. Add a lump of clay, straw and paper and you have the things.
Here is the (as usual, well researched) booklet:
More Things of Science scanned here.