- Use a large bottle
- Use a small lightbulb
- Construct the bottle around the lightbulb
- Construct the lightbulb inside the bottle
- Cut off and replace part of the bottle; this can be done almost seamlessly
- There's no technical reason that a lightbulb needs to be made of glass, so we can make a collapsing one, and unfold it inside like a ship-in-a-bottle
I remember E2 as (unofficial) predecessor of Wikipedia more than ten years ago . Back in the days Wikipedia also had a triva section - nowadays its forbidden , what a pitty. (good we still have IMDb and its trivia pages)
It's sad that Harry Eng's Wikipedia article redirects  to "Impossible bottle" article and Bulwersator removed the paragraph about Harry Eng two years ago .
 /. posts that made Wikipedia popular, "Everything2 Hits One Million Nodes": http://slashdot.org/story/01/03/29/2035230/everything2-hits-... , http://news.slashdot.org/story/01/03/02/1422244/nupedia-and-...
More seriously, note that he only claims the bottle hasn't been cut/modified, nothing about the objects within. To me, it's rather obvious that they're disassembled into pieces small enough to go in, then reassembled inside. Reassembly is the tricky part but it's not hard to see how things could be manipulated into position with string (or dental floss as he mentions), tweezers, sticks, and other tools.
There are some good videos of doing it on YouTube too.
(Also I observe that the "proprietary trade secrets" in this "industry" happen to be the complete opposite culture of the open-source/open culture/information sharing movement...)
So the bottom was cut open and sealed by heat then.
Some woods (including pine) are much more compressible than you might expect:
Instructions from the patron Saint of Woodworking: http://www.woodwrightschool.com/downloadable-plans/tooth%20a...
The others I looked at (playing cards, rubicks cube, ...) can be disassembled in smaller pieces that go through. That's his technique. So how do you disassemble a plank? I think it's a hollow piece of thin plywood (1 piece, no seams) that was soaked, folded up and then filled with something (resin).
Magicians do not often reveal their secrets, and I suppose some would even lie outright if you try to out them in public (although a good magician would find a way to ask you to stop ruining everyone's fun), but when a magician voluntarily tells you how something was not done, you can usually trust him. That's doubly true for respected magicians. I think it's a big part of what makes them respected.
Also, in the case of the bottles, cutting the bottom would not only be extremely easy to detect, it would also make the whole thing worthless. A cheap scam. Magician's consider themselves artists, not scammers.
Even if that's true (which it's not, according to the creator), there's no call to be so dismissive and superior about it. Seamlessly cutting and resealing a bottle is sure as hell not in my skillset, and I'd be pretty impressed by someone who could do it reliably.
Ignoring the wood for a moment, I'm focused on the padlock. Suppose it's not a real padlock. There are stripes on it which, to my eye, look like they might be corrugation. Perhaps it's hollow and can collapse like an accordion.
Edit: Or, per the description of the second-to-last bottle, the lock is broken down into parts and reassembled in the bottle.
Now, if you were to delaminate the lock's layers and reassemble it piece by piece inside the bottle with authentic-enough looking rivets, I can see it fitting through the neck without a problem, but I don't have an explanation for the solid piece of wood that large.
I think the padlock would fit if you took the shank off.
Have a lot of great memories thoroughly enjoying that book as a kid. Used to flip through it and test him through-out our sessions. Loved every minute of it.