I like to improvise, but I am not a jazz player on the horn. Nevertheless, it is a very good idea for any improviser to learn from any/every source and jazz is certainly a source that we should steal, uh, learn from at every opportunity. One basic resource for the jazz player over the years has been the so-called Real Book, which was for a long time an illegal compendium of lead sheets – basic melody and chords of jazz standards (and some not-so-standards). They were illegal because they included the (copyrighted) tunes. Fake books (real/fake? Get it?) that just gave the chords to songs without the tunes avoided this sticky bit of legality.
Real Books were hard to find for most people for a long time – you had to know a guy who knew a guy who sold them from the back of his station wagon in parking lots on odd Thursdays. Real Books were the necessary samizdat resources of learning jazz. If you know jazz, you could get together with anybody and play all night and beyond – somebody just had to call out the page in the RB and everybody could play, whether they were familiar with the tune or not.
Although you might be able to fault the usual Real Book for choices (lots of tunes you never heard of before) and mistakes in chords and melody, you can’t quibble over quantity. Lots of stuff here! RBs are thus handy but quite bulky to schlep around, which is possibly a good reason to learn the tunes by heart as quickly as possible.