Somebody on one of the many pregnancy related Facebook groups I belong to at the moment was worrying as she was late on in her pregnancy and hadn't even thought about writing a birth plan or packing her hospital bag.
Now, without trying to sound smug, I am ridiculously organised in everything and have literally been having to stop myself from writing my own birth plan until I reach 20 weeks! Of course, a birth plan isn't essential. You can go into labour without one and often even the best made plans can go out the window when the time comes as baby is firmly in charge (Cameron's labour was totally different from my original plan).
However, I think it is always a good idea to have at least some idea of what you would like to happen in labour in regards to pain relief, birth partners, cutting the cord etc. When you are finding it near impossible to even breathe through the pain of contractions, you won't be in a fit state to start reeling off your requests and might not even be able to answer basic questions. Having a written plan will ensure that as far as possible, the medical staff will be able to do things the way you want.
Writing a birth plan can be daunting, especially if it is your first baby. I would advise going online and doing a quick google search. This is all I did and I came up straight away with two templates which I have printed out ready for when I let myself start thinking about the birth!
I like how in depth the NHS template goes as it allows you to think about aspects of the birth which you might not have even considered such as delivering the placenta and vitamin K injections. It also includes a section on special requirements such as religious customes, special needs or the need for a language interpreter during labour.
Another good template is the HiPP Organic one which, although shorter, still has a lot of detail and is great as it looks a bit less scary and more down to earth. I aim to fill in both templates as a starting point and then from there write up my own personalised plan which I will make sure I have a copy of with my notes.
Also, don't be afraid to speak to your midwife about your birth plan prior to the birth. They will be able to answer any questions you might have about things such as the vitamin K injection (which can be administered to the baby via drops rather than the injection if you wish) and what pain relief would be best suited to you. It might also be comforting to talk to a friend or family member who has been through labour before (just make sure you let them know you don't want a horror story but advice on what you might want to write in your birth plan!).