I mentioned this term in the "Rope" post and I'd like to go into some more detail on it. What I mean by a "depletable" is something that is made unusable in the act of using it. Tape, glue, and staples were the examples I made before, but there are plenty others.
Guns, for example, are depletable, as bullets cannot be salvaged once used. I suppose if you were so inclined and so empowered you might be able to make your own bullets, but unless you're firing a musket and have a handy mine for black powder you can whip out of your pocket, I wouldn't risk it.
I would also put electronics under the header of depletables. However, having a hand-generator would take them back off of the list, seeing as you could recharge indefinitely. On the other hand, electronic devices are more difficult to repair than simple tools, so, overall, electronic use should be left to discretion.
The purpose of understanding what is depletable is to keep you safe in the long term. When something cannot be replenished, it would be unwise to rely on it. If I'm shooting game for food, I'll run out of bullets eventually, and because no one is around making more, that means I'm out of food.
Of course, the two exceptions to the rule are food and water, and those simply can't be avoided. Luckily, those aren't man-made, so they're not going to run out permanently; you'll just need to find more.
So now take a look at what you've got packed for the apocalypse. How much of that is going to run out on you over time?