For each publication, only a small subset of data is included in the forms of graphs. It is useful to deposit and share more of the data that was collected through https://datadryad.org/stash

The undergraduate physics curriculum includes laboratories. There are many experiments that are possible to be conducted at such a level and those experiments that I prefer include relatively simple setups, here is a list of experiments that I find useful:

1) Electrostatics: two charged aluminum balls

2) Dielectric constant using a aluminum foil for capacitive plates

3) Crater formation: dropping a ball into a sand box.

4) Pendulum period

The Physics GRE takes a bit of preparation, where "a bit" is approximately 6-12 months. The test is based on speed, therefore preparation for this specific test is of the essence. If you are pressed for time, you should also focus on those topics that have the most impact, see Wiki Physics GRE page. For example, there are 6 questions for laboratory methods and data analysis. For more ways to study, go to Alex Lang's website

In this day and age, there is not much need to store text books in bookshelves, as they are available in different sources, such as the LibreTexts for Physics or LibreTexts for Chemistry.  While not all topics are available yet, it seems more and more are becoming available, although there is still more needs for experimental textbooks, a few are available:

1) Online Laboratory (calculus-based introcutory physics)

2) Advanced Experimental Methods (on AFM, NMR, Lithography)

The number of physics journals is increasingly large. Here is a list of physics journals with high overall reputation: Scimago Journal Rank.

Additionally,  this is a list of questionable, scholarly open-access publishers:

https://scholarlyoa.com/publishers/

How to think about journal selection:

https://thinkchecksubmit.org/