about literature, i would advise you to start with alan watts. then move to mckenna.
if you have a solid philosophical education, you can jump right ahead to mckenna.
if not, (many people here won't agree with me, but it is what i think) read plato, nietzsche, even descartes, kant and liebniz. i find them always interesting to read,and that is what makes a writer great - the one who can stand the test of time.
watts, imho, won't stand as the time passes. as for mckenna, i am pretty sure it will influence many generations to come. as someone said in this forum, if only a fraction of mckenna's thought is true, he will be regarded as the copernicus of the mind. or something like that.
if you want to start, go for the LSD and the shrooms, and remember to start with baby steps (with small doses). although a strong dose at first can be fun after the trip has ended, it is no fun meanwhile it happens. but i don't find any fun in them even if i trip hard, or if i have an easy trip. they are teachers. they connect you with ... well, i don't know what they connect you. some say the overmind, some say the eternal now. some say the inner you.
i hope i've helped.