Can I fill it with whatever I can think of or only things I actually have right now?

I would bring a laptop with a good CPU and GPU, an ASIC Bitcoin miner and 10,000 in cash in case for some reason the miner broke or didn't work.

I would bide my time at pizza delivery jobs for 10 years paying rent living on ramen and buying small amounts of gold and silver coins. As soon as the first btc client was released by Satoshi I would start mining. I would be selling things on the cheap and performing services as much as humanly possibly. Id have a small gold and silver for BTC company, selling $50 gold coins for the equivalent of $25 in BTC at the time. I would not stop until I had at least 1,000,000 Bitcoin, or January 2017, whatever came first. As soon as the BTC rush of 2017 starts, I start selling my BTC en masse at the peak. Mail order, cash, in person, whatever. Claim what I need to on taxes. Sell the rest via an exchange before it's regulated as a security and needs to be taxed.

Now I am a big time multi-billionaire and no one even knows my name besides my financial advisors and closest friends from my pizza delivery days who now work for me doing "whatever the fuck they want" work for 100k per year.

I keep investing in companies who sell the most in online communications services (zoom, Microsoft, etc), mask production, hand sanitizer, laptops, gold and silver, and whatever else I can remember. As a ride out COVID, I've increased my 5-10 billion to 20-30 billion.

Now I live a happy "do whatever the fuck I want" life at roughly the same age I am now, only now I have total freedom and power because of "20 years of hard work and foresight -- I started as a pizza delivery boy, and you can too ;).”

Reflecting on my own actions and the folks I met on the way, taking a better attitude would help a lot. I was young and had good conversations with different types of people but did nothing with that for close to another 15 years.

We had much of the information then, IMO. And I remember talking with much older folks who were willing to listen to teens/young adults about a variety of topics. I just wasn't willing to say anything. Even to my peers.

I would take a better attitude.

A few useful books about electronics, devices and new inventions and all of the electronics I can fit into my backpack.

Like the other person mentioned their family, I would say that about my friends and other relations. I don't think it's possible for me to redo my life in a way that my decade old friendships would be the same (or even better) than what they became. I don't even know if I will feel the same about my friends if I decide to relive my life as memory is a precarious thing and I can't rely on how I feel about them to last until I meet them again and live life interacting with them while trying to change the world.

I could consider a 21yo body but as a millennial I would end up overaged for the people who were important in my life to have any meaningful relation with them.

I have considered the scenario of reliving my life, correcting my mistakes and maybe making some massive changes along the way, if I could somehow guarantee keeping the things that matter to me the same.

I forgot to write what things I would do, so here are some ideas:

• Investing is an obvious one which everyone else has also mentioned.
• I would download all the open source stuff, all leaked files, maybe even scour the dark web for stuff
• Buy NeXt to hire jobs as the CEO of my tech company (also any other corporations that I could buy back then, like Google)
• I'll create a note with ideas that were killed too soon or didn't last due to tampering by big corps, and products which got enshittified and implement them when there's no competition or wait for when I have enough money to not worry about people getting in my way.
• I'll create a note with mention of all the important events (multiple notes, encrypted, to prevent someone from using that information)
• Put an offline LLM and other AI on my phone (along with very reliable chargers and replacement batteries).
• (Kind of a sub point of above, but it got big) I'll try to take a phone with replaceable batteries and sturdy design. It would be great if it could fit in that time, I'll disable the touch screen to that effect and only use a stylus, and other changes to make it seem worse or maybe take a "bad" phone from the start. I'll also claim it's an experimental product if someone asks me about it.
• A list of my favourite recipes, so that I can be a food trailblazer
• Start my own music company and invest in artists which I know will be big in the future, give them better terms than my competition and use that roster to prepare for streaming. I'll already have Jobs and Ive to design iPod and take over that period.
• With RISC-V as my chip, I'll buy one of the fabs which went under back then and use it to establish myself as a chip manufacturer and once I have built up enough lead in the fab business with knowledge gathered before going back I'll open source RISC-V as an act of benevolence according to the world (I'll discuss the future fab knowledge with the researchers I will acqui-hire with the fab, they should be able to create something in a few years with whatever knowledge I can provide, I'll just have to act as a layman with more knowledge and if I go with my age they'll think I'm a smart kid)
• I didn't mention crypto because that might change with the chip info I bring back, so I'll see if that happens again and invest early and secretly to have enough of it to have a hand in that too.
• I'll also try to keep my identity hidden so that I can live the important parts of my life again as they were, and once I have lived those I'll consider if I need to be known to the world.
• I'll prepare media organizations to fight disinformation
• I'll bring back innovations in renewables that I'll slowly release into the world.

Winning lotto numbers for years.