|If you were suddenly dropped into a low-tech society, let's say medieval England or worse, with only the clothes on your back, how well equipped would you be to set yourself up with a decent life? What would you do?|
Many people's first thought in that situation would be "invent gunpowder". It's not a bad idea, but are you sure you could? Do you know what the ingredients are? Do you know what they were called in medieval England? Will you be able to get them or make them in medieval England? And having done so, what are you going to do with it? Gunpowder is pretty crummy for demolition, it's mostly good for launching projectiles, and you don't have a gun. Are you capable of making a rudimentary gun, or explaining to a blacksmith what to do? The original rudimentary guns had a habit of exploding because they were made from inferior metals. In medieval England, all you can get are inferior metals. Is your exploding gun actually going to be better than a crossbow or longbow? The only things that you can really do valuably with gunpowder, assuming you can make gunpowder, is make cannons, which are feasible with inferior metal if you can persuade someone to let you use that much, or impress people with your magical bright flashes and smoke. And are you sure you really know how to make and use cannons?
What else can you do with science that you have in your head? You might be able to make a rudimentary steam engine, if you had something worthwhile to do with it. Maybe use it for a powered battering-ram? Maybe you have enough science in your brain that you could use it to generate electricity - but what would you do with electricity? You could make magnets, I suppose, or separate water into hydrogen and oxygen. With collected hydrogen you could maybe make an extremely vulnerable oilskin zeppelin. Perhaps that would have some value. Assuming you can manage to finagle all the requisite materials.
After some thought, I came up with a much better answer for what I would do in medieval-world (which would also work in significantly lower-tech societies) - glass. I know how one makes glass. It only requires temperatures of around 1000°C, which are relatively feasible. The only ingredients you need are sand, lime and potash. Sand and lime are both readily available; decent potash requires a wee bit of chemistry (okay, I'm cheating slightly in that I didn't know this until I looked it up, but I do know it now). It's little more complicated than burning some wood and boiling some water. None of the ingredients are at all hard to come by.
But what good is glass? Well, for a start it's probably pretty valuable stuff in your low-tech society, so if you can find a buyer you're sorted without having to do anything else. But that's not where I want to be. No, my idea is that with my glass I can easily make mirrors. Once again, with a buyer for those I'd be made, but no, that's still not where I want to stop either. You see, once I have access to mirrors, I can make a solar furnace. The first use of a solar furnace is that I can now get those 1000°C temperatures without having to use any fuel. The even better use is that with a big solar furnace you can easily make temperatures higher than that - high enough that you can melt iron, and thence make steel, largely unavailable at that time because burning things didn't offer sufficient heat. There's also other related options, for example, a couple of thousand individually-aimed one-foot-square mirrors provides enough heat to crack stone or near-instantly ignite wood at a distance of 100 feet, for which I'm sure some military use could be found.
Once I've provided myself with glass, another thing I'm pretty sure I can make with my little flimsy bit of scientific knowledge is a distillery. Like the glass, that's an excellently dual-purpose item. Well, single-purpose - making extremely strong alcohol out of rudimentary materials. The alcohol, though, is dual-purpose - you can get people extremely drunk, for which ability people will likely pay handsomely, and you can (using the alcohol and the glass together) make Molotov cocktails, another lovely weapon with which to endear yourself to the monarch of your choice.
So, back to the original question - if you were suddenly dropped into a low-tech society with nothing but the clothes on your back and the knowledge in your head, what would you do?