If you do not have time to write down exactly what you just ate, but still have an idea of the calories and macros of the meal, you can quickly add it to your Diary using the Quick Track feature. This is how it works: 

1. Go to one of the meal cards under the journal.
2. Press the three little dots in the top right corner.
3. Press Quick Track.
4. Add the number of calories consumed.
5. Add macros if you have them. *
6. Add a title for the food/meal. *
7. Press Track.

* = Optional step. 

Note that each field, except the title, has a 5 character limit and does not support decimals.