Do you believe it's possible to hallucinate something which isn't real?

True, but none the less, the cube is still imaginary.

Most religions use drugs in some way during their practices. This is to encourage irrational thought and help convince themselves that their superstitions are true. This is most obvious in primitive religions where the practitioners enter into a fully intoxicated state and experience hallucinations. These hallucinations they assume to be divine in origin. As well as drugs, many other techniques are used by religions and cults in order to discourage rational thought, such as repeated chanting and/or the telling of hypnotic stories.

Most societies use drugs in some way.

And actually, most fundamentalist religions strongly discourage the use of drugs, since their own practices often rely on nobody in the religion having any alternative way to get high.  So, like Pentecostalists, their only buzz is going into something like an epileptic seizure while rolling around on the ground spastically and "speaking tongues." 

If they had a better way of getting a buzz, they probably wouldn't be into spazzing out and flipping around on the floor screaming gibberish.

The same could be said of the 9/11 terrorists, all in an Islamic offshoot that forbade them from just getting drunk or high.  So their buzz was knocking down the Twin Towers. 

Everything is a hallucination, either nothing is real or everything is real.

So explain to me why you can't hallucinate money to pay off your debts, or hallucinate yourself a new car or motorcycle? Or does this mean that nothing in the universe is real?

I once knew a guy who practiced various types of meditation.  He was very serious about it to the point of doing several hours per day for years on end.  He also claims he systematically taught himself to lucid dream.  He claims that one time he somehow woke up from his dream wearing a shirt that he created in his lucid dream.  While I can't in any way verify this claim and would tend to believe it's false, nothing else about this guy gave me any indication that he was crazy or a whacko, and in fact he was a good musical composer and highly skilled in martial arts (he practiced fracture training to build up his bone density and toughness).

Edit:  While I'm not asserting that the guy's claim is true, I think it's worth considering that you have probably never known anyone who has committed literally thousands or tens of thousands of hours to mental training.  If you stick a bodybuilder next to a regular guy, everybody and anybody will automatically recognize the bodybuilder as a superior physical specimen capable of feats of strength and endurance (e.g. dead-lifting a car) that the regular guy would consider impossible.  Isolating this information, it's plausible to assume that someone who commits to training their mind with a duration and intensity similar to a bodybuilder may be capable of performing feats of the mind that the average person would think is impossible (e.g. directly extending the effects of mental processes upon physical phenomena beyond your own body).

Is this a serious question?  If so, it's not quite analogous as you're interjecting a 2nd subject into the mix, and this interjection requires certain assumtions about the metal capacity of the cat.

It's obviously established that mental processes affect our physical bodies which can then indirectly affect physical phenomena outside of bodies (e.g. I think about moving my hand, and so I do, thus turning the key to start my car which then enables me to drive where I please).  But is it possible to turn the key directly through mental processes rather than indirectly by first moving my body?  I'd say it's plausible.

You might settle for training cat to walk across the board without knocking over any pieces?

The brain produces a magnetic field. It thus does moves "stuff" beyond the body's structural limits.
Unless you consider this magnetic field as a part of the structural being. In which case a more detailed definition of "structural limits" would be useful.