I don't think these are clues pointing to Rios being a hologram, it's a pretty massive reach to try to make them so.
Reading a philosophical book about life and death? He has been shown to have deep-seated issues around the violent death of his former captain, so the book relates to his struggle with that - a very human reaction.
He did not seem happy about Picard automatically assuming command, he simply did not overreact - he gave a very pointed look the first time and Picard backed down at once, and the second time was in a fraught combat situation where not engaging in even a minor power struggle was the correct thing to do, especially since Picard was advocating a course of action he agreed with (and let us note that Raffi didn't comply until Rios confirmed the order). His reaction isn't evidence that he is secretly a hologram, but rather is strong characterisation, showing us what kind of captain he is - calm, measured, patient, not prone to losing his head in a crisis or to overreacting when elderly passengers long-accustomed to command (and who he secretly admires) default to giving orders in times of heightened emotion.
There is no evidence that the medkit was anything but what it seemed: a medkit, transported to the location where it was needed, as was his drink - which he offered to Picard, let us remember, so that was clearly not holographic.
There is absolutely zero evidence that Rios is a hologram, while conversely, all evidence both on and off-screen is that he is human.
Okay.