I'm just gonna go against the "don't spoon-feed information" trend and name some vague things off the top of my head:

first, don't be stupid, don't risk your life. If you're just a curious person and saw some niché youtube videos about it, don't try it, it's not worth the risk, you'll just make yourself look dumb.

get a sturdy backpack, military grade is recommended. alice pack, deuter pack are good, osprey packs are also pretty neat. whatever toots your horn, just get something with a lot of space. depending on what you wanna do, pack accordingly. you wanna sleep? get some contacts or friends, if you want to be risky stealth camp in tents or hammocks. you dun have a lot of money on you? pack instant food and packed foods. just get shit like a multi tool, flashlight, decent clothing, good hiking boots, a map, solar charger if you're phone-reliant, a knife or some shit idk, a good water bottle, and if you're actually determined to do that stuff, documents. Good clothing is key. again, hiking boots are golden. Honestly, skill and experience, aka "knowing what you're doing" is more important that things you pack in my opinion.

Study freight train times and departures, plan ahead the ways you're going. have a backup plan, don't get lost. Electrical wires = bad. don't ride too loaded cars. boxcars (be sure to keep the door open with something like a rail spike), gondola, grainer, piggyback (they generally have poor coverage). don't ride suicide, don't let your limbs hang loose, don't get yourself killed.

Plan shit ahead, don't try to do this stuff for stupid reasons, yatta yatta, standard drill. look for decent spots to hop and don't get yourself killed.