Don't panic
You will panic as the realisation sets in. You have cut off your link to life. Take some deep breaths. Think.
Don't try a rice bag
The advice to me when I put my iPhone in the washing machine was - put it in a bag full of rice and it will dry out. It didn't. And I wasted a day, a whole day, in getting to an iPhone which works.
Don't tell people about it
People aren't interested. Or they are too interested and spend hours telling you about their iPhone tragedy. Keep it to yourself. Let them know they may find it difficult to contact you in the next few days.
Don't buy the cheapest cellphone to use while your iPhone is being mended
You will still need texts and calls. It is sheer hell wondering whether people are texting you and you are missing them. I know...
Make sure your substitute phone works in your house/flat/castle
I spent five days hanging out of my window to get a signal, telling my neighbours my innermost secrets and confidential information because, yes, I went for the £24.00 deal on the substitute phone
Don't run round in circles trying to find a way of getting a mended phone within a day on the basis you can't survive being cut off from life for any longer
I tried the Apple shop (no appointment for five days), went round all their approved service centres who had equally long waiting lists until finally accepting it was either a new phone or it was going to take five days for them to mend it. If it could be mended. Also don't sob as you tell your story. People will look upon you pityingly.
Don't rush out and buy a new one
You may think you can't exist for a week while your broken one is mended, but actually you can. And there is quite a big cost difference.
Don't think you will insure your mended phone and then forget as soon as you get it back
Think about it logically. How much is the insurance? How often have you wrecked your phone? How much have you paid to have it mended? Which is the best deal?
Don't forget about how your iPad isn't properly calibrated to get texts and emails as soon as you get your phone back
Take an overview of all of your devices and make sure that if one goes down, you can survive on the others for a while.
Get a landline
Old-fashioned I know, but in a world where the phoneline delivers your cable network, it is only a handset and a number, and boy, will you be pleased you've got it when your next iPhone disaster happens.....