Mycology-since about age 3, taught myself via reading every mushroom book or field guide I could put my grubby little mitts on, then went out with my old man taking me to walk in the woods, so I could pick wild mushrooms to eat.
Likewise botany....lol I remember one time while I was walking w/ my mom to primary school...and she very foolishly bet me twenty quid that I would be unable to correctly identify some plant spp. or other. A lot of money to a kid that age which wanted lab supplies, so I promptly ID'ed it
chemistry, both inorganic and organic. As a little wee bairn its always been a passion of mine, again I'm almost completely self taught. Pyro used to be so much fun. Lol I used to be a bit of a terror in that dept. Blowing up toy soldiers, blasting dolls into little bits, seeing how high of a fireball I could get from butane/propane, or if I really wanted to make a bang, then acetylene tanks, stuffed into a bin bag full of sodium chlorate weedkiller/sugar mixture.
Technology in general also, be it nanotech, nuclear physics, especially medical science, computer science, cognitive neuroscience, pharmacology, etc.
I want to get into genetics myself, teaching myself, build my own equipment-electroporator for introducing genes into cells, PCR thermal cycler, gene gun, electrophoresis chamber, centrifuges etc can all be built by hand to avoid spending huge sums on kit online, so I can make my own transgenic organisms. DMT-producing E.Coli for instance, or morphine-producing fruit. 'twould be lovely to be able to bite into a crisp, juicy apple, knowing it was packed full of morphia.