Disclaimer: I do not own Doctor Who or the song "Yes! We Have No Bananas" I am merely borrowing them for my own twisted enjoyment.

This is not any particular companion, just a random person traveling with The Doctor.

/

There are instances in every companion's life they contemplate taking out the insane Time Lord themselves. It may not cross their mind often or for very long, but it inevitably happens.

"There's a fruit store on our street
It's run by a Greek.
And he keeps good things to eat
But you should hear him speak!"

Rambling, one of the things a companion learns to deal with, or be driven insane by. Usually there is necessary information berried under the pile of words, or at the very least an interesting anecdote. You know from the very start about the rambling.

''When you ask him anything, he never answers "no".
He just "yes"es you to death, and as he takes your dough"

Danger, another of the list you know you will encounter regularly in such a life. You learn quickly that danger is not only physical. Psychological danger comes after The Doctor and all companions just as regularly as any bodily harm. The body can be healed easily, but the Doctor himself is proof of the mind and heart being far harder to fix.

"He tells you
"Yes, we have no bananas
We have-a no bananas today.
We've string beans, and onions
Cabbageses, and scallions,
And all sorts of fruit and say"

Jail cells, one of the most common stops on any given planet. Not something you know when joining the TARDIS crew. Though after the first one, two, or five, you realize locking up the Time Lord, and anyone he is with, is an extremely common pastime in most places.

"We have an old fashioned to-mah-to
A Long Island po-tah-to
But yes, we have no bananas.
We have no bananas today."

Bananas, oh bananas. One of those things no one warns you about. No companion will ever look at that particular fruit the same way again. He always seems to have one on him, yet never produces one when one would actually be useful. Need to make a banana split? You know who to ask. Locked in a cell and hungry? It never crosses his mind to produce the produce.

"Business got so good for him that he wrote home today,
"Send me Pete and Nick and Jim; I need help right away."
When he got them in the store, there was fun, you bet."

Companions should always be expecting The Doctor to pick up more companions, or at least realize there were some prior. Why so many blink and get confused at the idea is rather funny, even to the people who are blinking. After all he can't save all of creation on his own, every companion knows this, for every companion saves the Time Lord's life at some point.

"Someone asked for "sparrow grass" and then the whole quartet
All answered
"Yes, we have no bananas
We have-a no bananas today.
Just try those coconuts
Those walnuts and doughnuts
There ain't many nuts like they.
We'll sell you two kinds of red herring,
Dark brown, and ball-bearing."

But REALLY, of all the things to be warned about before taking on such a job as companion to the most amazing insane destructive hero in existence, the SINGING should be on the list. Not that he is a bad singer, no he can sing quite well when he wants to. Unfortunately now was not one of those times. When he said he had a plan to get out of this jail, a good companion should know better than to think it would be a SANE plan. If it works, I am going to kill him.

"But yes, we have no bananas
We have no bananas today."