Which foods or drinks are reusable?

Solution 1:

As a general rule, all reusable food items are now classified as Toys in Legion as opposed to standard items.

At present, the following food items are reusable:

• Ba'ruun's Bountiful Bloom
  • Only works on Draenor
  • 5 minute cooldown
• Tasty Talador Lunch
  • Works everywhere as of Legion
  • 15 minute cooldown
• Bottomless Stygana Mushroom Brew
  • Only works outdoors on Draenor
  • 20 minute cooldown
• The "Devilsaur" Lunchbox
  • Only works on the Broken Isles
    • Notably does not work on Argus
  • 15 minute cooldown

Solution 2:

Unfortunately there is usually no clear ingame indicator to which consumables are reusable and which aren't, however if it is reusable it's almost guaranteed that it has a cooldown, otherwise you'd be able to use it constantly and never needing to use expendable ones (unless it's significantly less effective).