Fighting Knives

Any knife you have when you enter into an armed conflict is a fighting knife.  With that in mind, does the knife you carry regularly meet your requirements for a fighting knife?  Do you even have any in mind when you purchase and carry a knife regularly?

How about this - following are the minimum requirements I have for a knife I carry on a regular basis:

• Long blade length (minimum four inches)
• Thick blade width (must withstand breaking during extreme thrusts)
• Robust handle and locking mechanism (need to be able to hold it securely with and without gloves)
• Inexpensive (expensive enough to be made well but not so expensive that I won't leave it behind)

Those are my basic requirements - what are yours?