How to decide whether the amount of study material provided to students is enough?

Arguably the most time-consuming component of teaching is preparation of study material (especially when in comes to a fresh lecturer of a new module).

1. First of all, every presentation should have slides. Who takes a lecturer without slides seriously? (with the only exception of, perhaps, really senior professors). If one dares to use a black- or whiteboard, students will take pictures on their iPhones instead of following the lecture, pretending they will follow it at home, which they never do. And students who miss the lecture will complain, since the slides are not available.
2. Secondly, some question / exercise sheets are important to keep students entertained and busy in class / tutorial.
3. Question sheets imply answer sheets, with (some) of solutions worked out, to help students prepare to the assessments.
4. Lecture notes, to collect all relevant information in one place, and save students some trouble looking for it in various textbooks. Helps with those students who are hip enough to never use a library.
5. Practice instructions, to carry out lab classes.

This is just a basic list, which comes to my mind, and I'm sure that other types of study / supporting materials are used in teaching.

I've heard rumours about some loci amoeni universities in the US, which provide their lecturers with all (or most) of these materials, professionally prepared by academic publishers. Apparently, this is not the case in the UK, at least not at every university. And I can now appreciate, that preparation of all these materials to every lecture / tutorial class can take a very considerable time.

Question: How do we decide, which materials are the most important for the class, and which are not? How do we assess, that the amount of materials prepared is sufficient?

Specs (by popular request): I am teaching Maths at BSc and MSc level in the UK. However, I would appreciate answers regardless your discipline / profile.