how does the narrator compare the boat to the boat of life?

J says that overpacking the boat.... like overloading our daily lives takes away the simple pleasures. He says that to truly enjoy life, we must cast away the unnecessary in order to enjoy the things we've been blessed with..... family, friends, music, and freedom. 

It is lumber, man—all lumber!  Throw it overboard.  It makes the boat so heavy to pull, you nearly faint at the oars.  It makes it so cumbersome and dangerous to manage, you never know a moment’s freedom from anxiety and care, never gain a moment’s rest for dreamy laziness—no time to watch the windy shadows skimming lightly o’er the shallows, or the glittering sunbeams flitting in and out among the ripples, or the great trees by the margin looking down at their own image, or the woods all green and golden, or the lilies white and yellow, or the sombre-waving rushes, or the sedges, or the orchis, or the blue forget-me-nots.

Throw the lumber over, man!  Let your boat of life be light, packed with only what you need—a homely home and simple pleasures, one or two friends, worth the name, someone to love and someone to love you, a cat, a dog, and a pipe or two, enough to eat and enough to wear, and a little more than enough to drink; for thirst is a dangerous thing.