I have one of the old saddleseat equitation books (since that's what I rode) and everything is highlighted, underlined, with tons of notes in the side margins or quotes. Sometimes this way of "destroying" the books makes them all the more valuable to you!
Oh I am absolutely bringing a pen and a highlighter. I am always hesitant to put that first mark in the book, but once I do it I love it. My brother found my summer reading book from senior year, as he is going into senior year this year, and he said my notes were helpful for the first half.
For the second half, I would just underline funny or weird phrases and write "ha". Apparently I got bored of actually annotating hahaha