Did you get it right?
The picnic has hot dogs, buns, ketchup, relish, onions, potato salad, lemonade, plates, and napkins.

The Answer
The correct answer is: mustard.
Here is why
- The hot dogs and buns are ready.
- Ketchup, relish, and chopped onions are present.
- The side dishes, drinks, plates, and napkins are ready.
- There is no mustard bottle, jar, packet, or mustard on a hot dog.
Why people miss it
The red ketchup and green relish make the topping area look complete, so the missing yellow condiment is easy to miss.
What answer did you get before checking?