I browsed over some of them, but certainly have not yet had a chance to look over everything. There’s plenty of letters from Einstein and family members. I found a particularly interesting letter from a head of an institution, to another program head. He says he does not recommend Einstein switching schools during his studies “even if he is a so-called ‘child prodigy.'”
There’s old report cards in the archive. A note recommends that Einstein look into private tutoring for French, history, and chemistry. There’s a comment from an inspector on a music exam after observing students playing violin:
One student, by name of Einstein, even sparkled by rendering an adagio from a Beethoven sonata with deep understanding.
There’s plenty of proofs that I’m sure will be interesting to those involved in math. (Couldn’t tell you). I also found some of his papers interesting. In one paper he discusses land formation based on glacier movement and friction.
I only had a quick look at some of the items. There’s plenty to go over. You could spend hours. For those interested in the life of Einstein, or science or math, this is a great free archive.