I’d use my knowledge of the future to do two chicks at the same time

Double entry accounting system.

I’m an accountant by trade. The double entry system wasn’t invented until the 15th century.

I could account for any lords various assets, goods, and livestock in an efficient, reliable and accurate manner

Assuming I am physically in the same place, I will fall to my death. If I somehow survive the fall I would be severely injured and alone in the wilderness. Within a few days I would probably die of either my injuries, dehydration, or hypothermia.

Wash my hands

As an Australian I would struggle significantly unless you were to also transport me geographically.

I would kill everyone I meet with the plagues I carry which I’m immune to.

You would die. There are many, many examples of explorers from “advanced” civilizations getting shipwrecked or stranded in an area where primitive hunter-gatherers live. Unless they are saved by the hunter gatherers, they are doomed, despite their knowledge of science and technology. Joseph Henrich talks extensively about these examples in his book, “The Secret of Our Success”

Check out this video to get an idea -> https://m.youtube.com/watch?v=jaoQh6BoH3c

I would teach London children the most obnoxious brain rot slang from today as a laugh.

Nothing. I’d sit under an tree and enjoy the peace and quiet. No trump. No DC. No MAGA. No reporters. No non stop ads. No social media. No Google. No Elon. No bezos. The list goes on. Sure I’d probably die of some random disease or bandits. But I’d be okay with it at that point.

I would pretend to be super-religious. Throughout the whole of human history, pretending to be super-religious has always been a viable path to survival and personal advancement.

Apart from that, I’d probably just die.

Wouldn’t I be in like empty space?

Probably die

Basic geography could go a long ways, if people believe you. At this point people were exploring the world trying to find the spice Islands, but didn’t know WTF they were doing. Magellan navigating the strait that would be named after him was impressive at its time, but now we know the best way from Europe to Asia (and spices and stuff) by sea without any modern canals is by going around Africa. Like, it still sucks and it’s a long trip but it’s doable compared to going to damn near Antarctica.

This assumes I don’t die, can communicate, and am not in the then-unpopulated (and quite landlocked) current location of Denver, Colorado.

Edit: bonus fact: if a sailor managed to smuggle a knapsack full of cloves back, it was worth about as much a house

Try to find the nearest shaman, apothecary or herbalist and trade my future clothes/pocket contents for some hallucinogens and painless poison. I ain’t living through a time before electricity.

Edit: I’m taking the middle road here and assuming something around year 1250 or so, not 1100 or 1400 as confusingly set in OP.

Okay, so unlike most other scenarios, I think I would be fine for a while at least. The peoples living where I live would have made and kept more or less regular contact with the sons of bitches from the south that would later crusade us (or I think maybe one of the crusades is presently ongoing at the time…) so while I would both introduce and be hit with diseases or more likely strains of familiar ones new to my body/their bodies, I think it wouldn’t be as destructive as entirely separated landmasses like America vs Europe.

So if I survive the shock my body gets hit with, and I don’t kill everyone around me, I think I would be fairly well received. As far as I’ve read, the languages and dialects were different than after the formalization of the written form, and at this time these lands were just starting to get forced under Swedish rule, so with my basic understanding of Swedish and of course my native language, I think I would be able to communicate well enough to not get instantly killed as a demon or something.

I think my best bet would be to introduce myself as some sort of demi-god, a bastard son of the god of forests and the hunt probably, which would hopefully explain my alien attire and materials used to make them. And the alien accent/dialect of both the local language or Swedish, depending on where I’d land. If the first contact I make aren’t local but crusaders, I suppose I’d have to try and push myself as a wandering preacher of Christ or something. I’d have to hope they’d speak Swedish, since I do not know German well enough to form two words together, and they’d likely be the next likely encounters. Novgorodians I think were fine with the Swedish language in general, so if our current knowledge of history was off enough that I’d meet them here, I’d still be fine. No idea what I’d pretend to be to them though. My limited knowledge of history doesn’t help there. But as far as I understand, they were sort of a melting pot of close-by cultures, and not so focused on these lands at this time, they’d just take me for a local hermit and let me run off clumsily.

If I was able to survive the first encounters and get myself to a village or a hillfort, I’d try and establish myself as a wise one, helping with calculations and engineering and whatnot to the best of my capabilities, which I would think honestly should far exceed those of the locals at the time. So maybe I’d get by just for being useful and knowledgeable.

But I don’t think I’d live a long life. These were a turbulent and violent time and one village elder or the other, fancying themself a king or whatever, would just send assassins to off me for being an asset for the local leader where I’d end up in.

Even if I’d travel to avoid this problem, it probably wouldn’t take until my old ages to have someone or something off me just by happenstance. And I wouldn’t want to live a hermit in a time where internet or computers aren’t a thing. I think the only way to cope would be to focus on a family, try and bring up children and have that fulfill my life as best it can, as long as it can.

Honestly, I consider myself lucky in this scenario. We still have our language alive and in use, the same the locals would speak at that time. This together with the general superstitious nature of the local tribes — which the crusades and Christianity, with overt blood and sadistic violence, would (thankfully later, I hope for my sake here, at least according to our current knowledge) succeed in some amount to water down and turn them to its specific flavor of lame ass superstition — would make it probably at least somewhat likely I wouldn’t be killed on sight or something to that effect.