Our protagonist was a intelligent, good natured, programmer who just tucked himself in bed at the end of celebrating his 35th birthday, only to wake up as a child on the day of his fifth birthday party, apparently 30 years in the past.
After going through the original disbelief, questioning of his sanity, and similar issues he resigned himself to accepting this is his world now and chose to utilize his knowledge of the future to live a better life. Early on he finds himself enjoying being seen as a prodigy for how quickly he 'mastered' his early school subjects, though as he reaches high school and college he reaches a point where he can no longer depend on his past education to score easy A's and finds himself not enjoying the disappointment he gets for 'not living up to his potential' as the prodigy he was presumed to be as a child.
However It's when he is graduating with his new degree in computer engineering that he finally gets informed why he is traveling in time, and that it will continue to happen. His time travel will obey the following rules:
- He will go back in time when he goes asleep after his 35 birthday, which occurs on oct 2020, and wake up on his fifth birthday
- He will experience a minimum of 10 of these repeat lifetimes, and potentially far more
- Eventually the repeats will stop and time will continue as usual after the 35 birthday. He will know when the lifetime starts that it's his last repeat.
- He will not forget past lifetimes, despite the subjective centuries. This doesn't mean his memory during a lifetime is any better or he will be any better at recalling something from a past lifetime then he would have been at the end of that lifetime.
- Despite his mental age his thought processes are still is affected by having a child's body and mind. In his youth he will still enjoy 'childish' activities, struggle with controlling emotion & patience, and generally still have the temperament of a child despite his increased knowledge. Likewise he won't feel much in way of romantic or sexual attraction until puberty, and he gets to enjoy all the hormonal fun of puberty each lifetime.
- The butterfly effect is in full force. While he can use his knowledge of the future to predict, and change, events at first as soon as he makes a significant change the future will be altered significantly enough to make it hard to anticipate what will happen next.
- It is possible to pick small items to take back in time with him. The size and amount of items he can carry back is limited by both weight and physical dimensions, but with repeated lifetimes he will grow capable of transporting more back in time with him.
- At the end of his first repeat he can carry back something around the size of a thumbdrive, by his third lifetime he could carry a laptop, the size of things he can store will continue to grow linearly with lifetimes (possibly slowing down after he reaches a sufficiently large carrying capacity)
- Items he takes back in time will exist in a sort of Hammerspace until he needs them, preventing other's from asking questions about why a preschooler has an advanced laptop.
- If he dies during a lifetime he will wake up as a 5 year old again at the start of a new lifetime. Death is still quite traumatic, and he may lose access to items in his hammerspace when it happens, so it's best to avoid it.
Personality wise you can also take the following for granted:
- His family lives int he USA and is a non descript upper middle class family; well off but with no special resources or connections.
- From personal experience he has decided he doesn't like being seen as a child prodigy, since he can't live up to the expectations later in life, nor does he like the spotlight of media attention. Thus he doesn't want to use his future knowledge to become too famous or rich or be seen as a child prodigy. He is not opposed to being seen as smarter then average or being successful, so long as he doesn't attract too much attention.
- He is a generally decent person who doesn't want to utilize his knowledge to harm, manipulate, or exploit others. In fact he'd like to use it to help people and improve the human condition if possible; though he isn't a saint either and won't dedicate all his time to helping others.
- After numerous lifetimes he is going to start struggling with boredom, impatience, and generally going mildly stir-crazy, particularly during his childhood when expected to spend most of his life in school relearning things he long since mastered.
Our protagonist has decided that one of the things he wants to do is to make 'future' knowledge generally available in the 'past' once he repeats. By uplifting our knowledge by 30 years he hopes both to improve and save lives via making advanced technology available sooner, and to decrease his own boredom by making more modern technology, games, etc available sooner for him to enjoy. He hopes for a compounding effect, with each lifetime making new discoveries thanks to the bootstrapping of having access to his past lifetimes discoveries.
I'm looking for the best strategy he can utilize for transporting knowledge backwards, and sharing the knowledge with the general public.
Even with a few 'lifetimes' of experience our hero won't come close to knowing everything, thus he is mostly going to be dependent on carrying knowledge back by bringing something back in his 'hammerspace'.
Luckily he could fit gigs worth of documentation on his thumbdrive even at the end of his first repeat, unluckily he won't have a machine capable of reading a thumbdrive's data for decades. He's going to have to think carefully about what to bring back in time to trade off storage capacity with availability of technology to read the medium at first.
In terms of distributing the knowledge he needs to figure out a way to making the knowledge publicly available to everyone in a mostly pre-internet world of 30 years ago, all while somehow ensuring his own anonymity to avoid drawing the very attention he's learned he does not enjoy.
Finally he has to convince people of the knowledge's authenticity. How does he convince people this is not a practical joke and this stuff is real? Yes Higgs-Bison is real, you can clone animals and rewrite DNA with CRISPR, and everyone should be expected to be carrying around a 'supercomputer' in their pockets, that they mostly use to play floppy birds. While his claims can be validated with research, how does he provide sufficient evidence to both convince people of authenticity enough that they will take time to validate it, and how can he help them validate things as quick as possible so they can skip ahead to using it to building cool toys for him to play with.
I'm looking both for original strategies to bring back knowledge, when he can carry little back in time and needs to figure out how to bootstrap things, and eventual strategies for once he can carry more backwards in time, and had enough time to watch and perfect the information sharing techniques, that he can just carry back a perfectly built society uplifting tool with him to the past.
My final solution:
I ended up deciding I liked the idea of asking questions and making other's do the work of figuring out how to do things for me so much my character could do it to. He takes back as much as he can per the original accepted answer, but he does a poor job of picking and choosing what data is most important to bring back the first time.
Luckily he brought back enough to convince other's he was legit, and he had the forethought to preface it with a description of what was happening and a request for help designing a better process for his next leap back. By the third leap large non-profits start to be created dedicated solely to designing the uplift package he should take back on his next leap. He just has to pay for the uplift hardware they designed, upload the data they deemed worth transporting, and carry that back.