As you know, it is important to keep your resume updated even if you aren’t actively job searching just in case a great opportunity comes along. One thing that I recommend to all of my clients is to keep a diary or journal about what is going on at work. Did your boss tell you what a great job you are doing? Write it down. Were you just named Employee of the Month? Write it down. Is a co-worker behaving inappropriately toward you? Talk to your boss and write it down in your journal. Date each entry in your journal and keep your records at home rather than at work.
A journal can be an invaluable tool when you need to update your resume and start your job search. I can't tell you how many times I have tried to recall little wins or small steps toward a larger goal at work. It can be difficult to remember everything you had to do in order to get to where you are today. A resume should list your accomplishments both big and small so that you can illustrate your skills and value to a potential employer. If you keep good records of your accomplishments and the challenges you faced in achieving them it will be easier for you to tell your story on a resume when you need to.
Don't wait until you need to get your resume out the door to try to update it. Keep it current or at least keep a career journal so that you can update it accurately and quickly if you need to.