I have carried a large knife, a 3' long machete for trail cleanup, but I have never worried about getting it out quickly. Usually I slide it in its sheath down the tunnel under the side pockets, lash the belt loop on the sheath to the load control strap and catch the sheath under a couple of compression straps. Being 3' long it is really too long to pull out with my arms.

If anyone is dead set on carrying a Rambo blade you can use a drop strap so it hangs lower to avoid the backpack belt. Lashing it to your calf or boot is a popular choice for military folks. Any way you do it your going to look like a dork if you aren't in a combat zone, hanging with survivalists, or people pushing the mountain man look. There is no accounting for taste.