Others more autistic will probably be able to dump books at you. I wont do that. But I do have advice.
I'd start by asking them which shit they're interested in reading about, be it history, philosophy, theory, and what kind of stuff, e.g. about imperialism, or class, or what. This is somewhat important, because you can get a feel for what's accessible based on what background they have and where they feel they want to add to. Try to challenge them ofc, but there's some stuff that's theoretically advanced and really good, but maybe boring, and some stuff that's more fun and easy reading but won't necessarily give them all the necessary tools to come to a materialist, dialectical view of the world. So it's kind of a trade-off of how theoretically sharp and unified you care to be, and how much background you have to give first. To me though even just talking this through narrows it down for me because really everyone needs context in order to understand the theory.
I can tell you that some pop-marxist works like White Trash by Isenberg are pretty good for baby-leftists, just in developing a class focus and a more thorough understanding of history. I'd also focus on books that get into the "hidden history", i know Zinn's People's History was one that made a friend of mine a life-long leftist, and I like William Blum's books on the CIA and american imperialism. I'd not touch on whatever hot marxists honestly, or marx himself, unless people are really wanting that. I wouldn't touch meme shit with a pole either like D&G, afro-pessimism, or settlers.
Honestly the more i write the more I'm certain: Focus on getting them history mixed with good class analysis. That's literally it. Vet the books first, make sure they're not some weird frankfurt ivory tower shit. That's it. Because people are gonna go off and take their own path eventually, learning for themselves. And there's a million pamphlets, programs, economics books, critiques + refutations, and philosophical tomes, but most importantly is a deep history of the world and class society. There's really nothing bad to read, but if they go down some anarchist or wokoid tangent early then they'll waste a lot of time on a sort of pseudo-radicalism, and might just get tired of it and think there's no way forward and give up. But honestly it's not that high stakes, people can read weird shit, go down rabbitholes, and will definitely emerge on the other side enriched. But once we get jobs and shit our ability to learn takes a nosedive since there's so much less free time, especially if you want to hang out with friends too.
Also don't shy away from Lenin and Stalin. They wrote shit in pretty accessible ways. Lenin's "Karl Marx" is really good, maybe even start off with that because it's a really solid foundation. But really just focus on giving them history, like deep and broad history if possible, and with a class analysis or at least a anti-imperialist angle.