Food
Easy; simple
Ill or sick
Under the weather
To understand something complicated
To wrap [one's] head around [something]
To get something exactly right
To hit the nail on the head
To tell a secret
To spill the beans
The worst possible situation
A perfect storm
To get cold feet
In good times and in bad times
Through thick and thin
To not take [something] so seriously
To stop being careful and do something crazy
To throw caution to the wind
Without thinking about something carefully
Off the top of [one's] head
to do something difficult/unpleasant that one has been hesitating over.
To bite the bullet
To quickly summarise
In a nutshell
Good things come of bad situations
Every cloud has a silver lining
To ignore or be hostile [towards someone]
to give [someone] the cold shoulder
To add insult to injury
The basics/necessities
The bread and butter
To be overly busy/overwhelmed by tasks
to be unable to act freely because something prevents it
To have [one's] hands tied
To go back to the start of a process
To go back to the drawing board