Now, many times while playing Tekkit and using the things you normally cannot use in real life (Alchemy bags, Nano-suit armor) I like to think of theories and such of how these would work.
The most recent one on my mind in that Nano-Suit armor is made of buckminsterfullerene, a form of carbon harder then diamond. Here is a video about its discovery: http://www.youtube.com/watch?v=xVZRGcg-BXI
I have had many other theories and ideas, not that they are on my mind now, but I plan on posting them from time to time. As for alchemy bags, I can think of nothing but collapsing space (Without collapsing the mass) which would require ridiculous amounts of energy.
I also think energy collectors could be made in real life, though not very effectively. In our very own sun, matter is converted into energy in the form of light and heat(hydrogen and helium smush into each other from the intense gravity, and then explode), so why can't we reverse engineer this? Well, the main problem is that small amounts of matter produce huge amounts of energy, which means we are going to need gigantic amounts of energy if we plain on making anything useful. Therefor, it doesn't make much sense to use the faint light of the world around you to make matter, which is what an energy collector does.
Until I remember my other cool ideas, that's it. I'll update every once and a while.