First off, I want to let you know that you are not the first person to ever have this fear. I have seen it many times over in new students and I experienced it myself when I first started. The good news, is as of yet, I have not seen anyone or worked with anyone who could not remember the pertinent information relating to the call. All it takes is practice. You should never try to find ways to get around an issue that should be dealt with by practicing. I understand you think you have poor memory skills, but you did just graduate from school successfully. It may seem a bit overwhelming now, but in a year or two you will realize how silly your fear was.
As for solutions, you have been given several great ideas.
Me personally, I always have a strip of tape on my leg to write on. I also carry a small notepad in my back pocket for back up. I hate bringing in the clipboard on calls, so that is why I have these two methods. If someone decides to refuse, no big deal...we could use the exercise anyway walking back to the truck to get the clipboard. This is also a good time to return some uneeded equipment. The reason I hate the clipboard is someone feels it is their duty to stand there and hold it at all times. I feel there are other things they could be doing as I do not need a scribe doing constant documentation.
Your fears about not having time to write things down is unfounded. You just need to find and develop a routine that you dont deviate from until you are more experienced and comfortable with obtaining patient information. As you are talking to the pt, you can be writing everything down. If your service utilizes a lifepak or any other monitor, the vitals are automatically stored anyways for retrieval at a later date. In a pinch, you can always scribble them down on the stretcher sheet or disposable cover.
The true solution and hardest one to teach is when interviewing patients, you have to LISTEN. I do not mean hear them, but I mean LISTEN to them. SO many students are so caught up in what they have to do next, they are not really listening to the answers the pts give. You have the time to listen and write as you interview patients. True ALS patients do not come along so often that you never have time to document while talking to them. On those occassions when you do have an emergency and must act quickly or the pt will suffer, do not worry because typically after these calls you sit down with your partner and rehash the details so that you may document properly. There is not too much for you to screw up right now as a basic, you are not pushing meds and needing to document times, etc. Your biggest concern is gathering history, meds and writing the vitals. Practice, Practice, Practice and you will do fine.