Reggie’s Outdoor has a great video about how to build a snare trap. This is a simple trap that can be easily built in survival situations.
http://www.youtube.com/watch?v=I24CHStwFt0 Hunteddown848 posted a great design for making an improved deadfall trap. These traps are simple and effective when properly constructed. Only use these in a survival situation, though (don’t just kill squirrels).