Jim created this step-by-step tutorial on how to create a hand-vise. Although he says it is great for holding bone & fishhooks, I am sure it would be great for plastics and electronics too. This is a really good addition to your toolbox, even if you are not a survivalist.
A small, easy-to-use handvice can be readily made out of a one-inch thick hardwood limb. Such a vice is very handy in stone and bone working. It can be wedged between two rocks or in a tree trunk to provide a very steady holder for small projects (arrowheads, fish hooks, etc.).
Make your own hand-vise – Link