Which nuts can be cracked without tools?
Yes, you can squeeze walnuts, pecans, almonds together and get something going.  I won't mention peanuts because they're not tree nuts (and they've lost my respect in other ways).  Read this answer tongue-in-cheek given the gravity of the question.

Obviously pistachios are the easiest to open and filberts/hazelnuts the tougher nuts to crack. Pine nuts are somewhat easy, but who wants to carry a barrel of pine cones just to get a few nuts?  I've never seen a macadamia or brazil nuts in a shell and been told Cashews aren't edible unroasted. 

You can also get creative using tools other than a nutcracker or your hands.  I used to use the door and jamb (hinge side) in college since we had indestructible doors.  Even keys and car keys are useful to wedge open walnuts.  Some birds (crows/ravens) throw the nuts on the road and wait for a car (hat-tip to them clever birds).  Pretty sure one of my friends uses his iPhone 5 as a hammer (it works, but don't do it).

Finally, if you're concerned about oxidization on shelled nuts, I understand.  As a delicious option, try placing shelled walnuts or almonds in cold water in the fridge overnight and rinse in the morning.  The skins slide off and most of the bitter washes away leaving pure yumminess behind.