常備

1. Origins, structure, and basic meaning

• Structure: 常備, read じょうび, means keeping useful supplies permanently on hand.
• Basic usage: 電池を常備している describes an existing stock; 乾麺を常備しておく emphasizes preparing supplies for later need.

2. Common pitfalls and similar expressions

• Existing stock and preparatory ておく
  • している presents the maintained state, whereas しておく foregrounds advance preparation.