Something you sit on that begins with K is your kiester.
A Yacht!
Kelp
kick
khakis
A knapsack?
Knife
Good ol "KOOL-AID"
Kill, Kiss, Spontaniously combust..... oh wait...
* kilt * knee socks * khaki pants * knee pads * kerchief
yes there is a film beginning with k it is called kramer v kramer
Kale, Kielbasa, Kiwi, Knackwurst/Knockwurst, Kohlrabi, Kumquat to name a few...