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.