Laws on owning and carrying edged weapons vary widely from state to state and even between smaller jurisdictions within states. Most of these laws will only be an issue for someone that is a serious knife aficionado. In California, (as of this writing) you can carry a single edged knife as long as it is not concealed. Double-edged knives can be owned but not carried. Carrying any concealed knife, other than a folding single edged knife is a felony. Keep in mind that most rifle bayonets are classified as double-edged knives.
Automatic (“switchblade”) knives are legal to own in a few states, but not most. (They sadly got a bad reputation due to some Hollywood movies. In actuality they are a useful tool.) Further, some states allow possession of automatic knives in a collection, but not pocket carry on the street. This is the case in (as of this writing) Montana, Texas, and Wyoming. For current details on various state laws, see:
http://www.amatecon.com/switchblade.html
With the recent profusion of new folding knife designs—many of which can be opened with one hand—there are practical alternatives to automatic knives, assuming that they are restricted in your state. I generally prefer liner lock and axis lock designs with half serrated tanto style blades. I buy knives in medium price ranges, from makers like Columbia River Knife and Tool (CRKT). Avoid any of the low-end brands and anything made in China! Also, since pocket knives often get lost in the field, you might think twice about buying a $600 custom knife. Frankly, I’d rather buy 15+ CRKTs for the same amount of money, but YMMV. I look forward to getting e-mails from some of you folks with extensive knife field use experience for your specific recommendations.