Don Boyer & sr15: I will keep that in mind.
KPopFever605: About my username - I just thought it was funny. Something serious/ominous/powerful (like necromancy) combined with some irrelevant/cheap/mundane (like french fries). Plus, it wasn't already taken.
Also, thanks for your reply. I hadn't even thought about evaluating the packets from that perspective..... that is, considering how close the packets are in the direction going from my chest towards the observer. Once I started looking at it that way, I noticed the 2nd from the top packet was kinda pushing against the middle card as I raised it up. So I am now keeping an eye on this and it seems to have helped reduce the problem. It's not perfect... but it is certainly much better.
sr15: Your point about positioning the packet further up the thumb did indeed end up helping me. (Thanks.) I unfortunately have an especially big/flat/wide thumb nail... which means I don't have as much fleshy rounded edges to work with.... but moving the packet up further helped me get a little less thumbnail involved. Which means I can grip it better to prevent the rotation.