The original question is actually quite difficult - One item people aren't thinking about. We're a bad group to consider that, since most of us have a pretty broad range of considerations.
The basic, unpowered entertainment / recreation items are likely the things that are most over-looked. Even those of us who focus on preparing, often are focused on "Needs" those things you simply can't survive without, forgetting that not every minute will be consumed with pressing survival and light entertainment will be vital. A friend of mine recently picked up an spring driven wind-up phonograph (acoustic record player) and more than a hundred vinyl records. It runs several hours on a single winding, required no electricity and provides a beautiful creature comfort that eases labor and improves recreation time.
But more important than what "everyone" is forgetting, is what you're forgetting. So here's my process for evaluating what I have, what I need, want and should invest in next - since we all have limited funds and unlimited ambition.
1) Make a list of possible emergency / survival events, then order them in terms of probability of ocuring. Include the mundane - Jobloss, Extended Illness or Injury, Personal/family emergency, etc and the more extreme - temperary loss of government control / public services, total collapse of government, natural disaster, etc.
2) Once you have a list of likely events, make a list of tasks each entails, resources for those tasks and time frames that you'll need to complete them.
3) Take the list of tasks, and make a list of materials, supplies or equipment needed to accomplish them.
4) Work down the list of tasks related to the most likely events first, the moving the less likely. They next thing you should buy is the equipment, supplies or materials needed for the highest priority task that's not fully met in the most likely emergency event.
Make the list, and work your way down. Review the list every 3-4 months to make sure you're updating as you learn more about possible events and tasks you might have to accomplish.