What is the best way to open thick clamshell packaging, like this:
I usually use scissors, but it's difficult when the plastic is particularly thick or the item is oddly shaped.
Wikipedia has a nice solution:
Tin snips are effective for tough plastics; the higher mechanical advantage of compound metal snips make it possible to cut such packages open even using little hand strength. These packages can also be opened with an ordinary household can opener.
I have found it easiest to run a razor knife / utility knive along two adjacent sides, avoiding the sealed edge. The plastic is very hard and durable where the seal is, but it is relatively thin if you move in a bit from the seal. Cutting along two adjacent sides in an "L" formation allows for easier access to the product, and helps to avoid getting cut by the plastic's edge.
You're probably not necessarily looking for the 'best' way to open it, but one that will work when you're in the middle of nowhere, you just purchased an item from a store, and for obvious reasons don't carry scissors with you.
Chances are you don't care for the cardboard packaging or imagery (and want to vent your frustration on a bad design). If you're out and about, one thing you are probably always carrying with you is a house key (if you use one of the square ones, you're out of luck).
On the flattest, widest part of the surface (double check there's no cables or useful parts underneath or hidden by the cardboard - physically feel it), apply the 'sharp' point of the key and cut up and down (preferably in the centre as a line). You'll have to repeat this process as a key is fairly blunt - but it does mean you will avoid any serious cuts.
Once you get a line in (the wider the open line, the easier this will be), place either hand or fingers like you would pull apart two curtains. Apply brute force and pull apart in opposite directions. What will happen is the line will further split and allow you to worm out the item and contents.
This might seem inefficient, but cutting a slot and pulling apart is sometimes actually easier than scissors, and it's a neat trick if you're in a remote area.
(If you don't have such a shaped key, it might be worth getting one.)