Rav Kook had three sefarim on his table in order to enhance his oneg Shabbos. 1] The Likutei Torah of the Baal Hatanya. 2] The Sfas Emes. 3] A sefer of pipul called Kli Chemdah written by Rav Meir Don Plotzky ztz"l, who was a contemporary of the Rav.
For the first sefer, it is a MUST to go here and read the Maamarim of the Rebbe with a biur. And/or buy "חסידות מבוארת". If you can't understand on your own then listen to shiurim or learn with a chavrusa. [BTW - Rav Soloveitchik was impacted deeply by the Torah of the Baal Hatanya - so his sefarim sefer are for YU intellectuals and otherwise as well:-)].
For the second - we have many a shiur on line. Here is the latest.
As for the Kli Chemdah - I never see anybody learning it and it is not quoted so often so BL"N I will try to bring him back into the public eye where he belongs. I LOVE Kli Chemdah. DEEEELICIOUS!!!
A note on "Open Orthodoxy". The Rav was Open Orthodox. A talmid of the litvishe Netziv in litvishe Yeshivas Volozhin who followed the Vilna Gaon in his halachic practice had three sefarim on his table - all written by Chasidishe Rabbonim. THAT is Open Orthodoxy. May we all merit to open ourselves to the Torah of Tzadikei Ha-doros of all streams [and of course not waste our time with much of the nonsense that circulates on the web].
