If you have a bag of unshelled nuts from the holidays and no nutcracker, you can use a bit of force and your hands to crack two nuts at a time.
YouTube user BeautyHealthTravel shares a technique for cracking two nuts in your hand. The surface of most shell nuts will have a side that is harder than the others. Put two nuts in your hand with the hard sides facing each other, firmly close your hand around the nuts and use your other hand to provide force that causes the nuts to crack.
I just tried this trick with a few pecans and while it didn't work as perfectly as in the video the technique did crack the nut open. I'm not sure how many types of nuts this would work with, but you can definitely use the technique with pecans and walnuts.