Every story contains props, from everyday items like wallets and keys to specialized weapons and enchanted amulets. Without props, stories are little more than talking heads in empty rooms.
Because your stories contain props, you must become a prop master. You must know where your props are at all times. If you lose track of your props, you lose track of your story. Lose track of your story and you lose your reader.
Here's an example:
On page 114 of the ROC paperback edition of Jim Butcher's Storm Front, the narrator "tossed the pentacle on the table," where it remains for the rest of the scene, even after the narrator leaves the building.
On page 280, the narrator notes that he still had his "mother's pentacle talisman" at his throat.
No, he doesn't. The pentacle remains on the table on page 114. The narrator never picked it up. He never returned to the building to get it. He didn't send someone to get it for him, and no one voluntarily brought it to him.
In this case, the prop master failed.
This mistake could have been corrected with a simple sentence along the lines of: "I grabbed the pentacle on my way out."
So how to avoid losing track of important props?
Start at your story's climax and identify every important prop--the pentacle, the revolver, the poodle, the red slippers, and everything else. Then, one prop at a time, go backward through your story and find each reference to that prop.
Make certain that your characters haven't left important props behind. If, for example, your character has a derringer in the climactic scene, and he stuck the derringer in his pants pocket in the first scene, make certain he didn't change pants in the fifth scene--and, if he did, make certain that he transferred the derringer to the pocket of the pants he's wearing at the climax.
So, to avoid missing and misplaced props, become a prop master.
Your readers will appreciate it.