To take over the world? I'd take the records of every international technology and medical patent. And, a cell phone. I'd get the local news interested in my new handheld PC, find the least scrupulous tech company which reached out to me, and hatch a plan to create a trillion dollar tech empire.

A modern desktop PC full with top of the line deep learning graphics cards.

I will flood the internet with helpful comments, exploits, anything that will take down the banking grid. I will sway online and print media discourse towards progressive politics. I will take down Murdoch media and ensure that he never again makes a cent spreading his rhetoric.

I will start a consulting company using my AI models as my employees and make unspeakable amount of money, whilst ensuring that large contracting firms never take off.

I will buy up large linear strips of country, and build railroads and rail stations everywhere, whilst building free accommodation above and below the tracks to ensure that the homeless always have somewhere to sleep, and to ensure that buy-to-let landlords can never return much on their investment.

I will crash weapon trading stock markets, exploit the emails of corrupt politicians and their billionaire donors. I will wage financial war on the 1% until the world gini index reaches 0.5

Pingy Putty and Reaganism would all still be in heavy effect, I can't think of a way any one person is going to bring down 3 nuclear super-war-states. We don't have any anti nuke tech eminence in shadow but nice writing prompt for potential suffering trying.

My phone, laptop, charging cables, ethernet cables, tons of SSDs to use with said laptop, Kali, and a bunch of cyber-sec resources.

Having a $2000 2023 gaming/workstation laptop would be an insane amount of computing power in 1999. Being able to use modern-day exploits and discoveries in 1999 would probably allow me to gather as much intel as I needed from my targets while not being discovered. If something gets patched by a Windows XP service pack, I'll still have an endless list of exploits that work. Hell, I'd even have access to something like Spectre and Meltdown, and that's something that still must develop organically.

I'm squashing my partner into a very large backpack and taking them with me.

I don't think I could take over the world so I choose love. But I can't resist the new body part which is why I'm not just staying here.

I'd take the entirety of the USA's military hardware. Nobody said how big the backpack was.

I assume I get ID for a person born in '78 if I choose the adult body? I was born, but very young.

Hard drives of data compatible with old computers, and a few modern laptops for good measure. Maybe some electronics equipment too in case I really need to interface with something obsolete or proprietary. Some period-appropriate cash to live on before my first "job". The 2000's won't know what hit them.

I'm not going to be able to take over the world (shit, even taking over Afghanistan proved to be too hard), but I sure as hell can be a shadowy hacker figure that steers the course of history. I'll probably avert 9/11 assuming I can get up and running fast enough, and try to steer China towards reform and detente with the West. Russia's probably intractable. I wonder if I could tip the Florida election towards Gore, in order to get global warming taken care of faster. Giving a bump to renewables research could also help things along.

Edit: So, there would be a lot of phases to this, as I gradually shift from being anonymous to a hot item. Once I reach some point at or after present day, I'll publish my archives so the world can decide for itself, and I'll leave proof early on that it's genuine, for example as hashes of data in things like newspapers that are well archived. Then I'll dismantle my cabal and retire.

1989 would be better. 2000s were pretty terrible.