How well do you know your gear? How many runs have you gone on using your gear? Have you figured out all the quirks? Do you even need the gear? These are all questions you should consider when it comes to the gear you run with.
I highly suggest running with the gear you will use on race day regularly. This way when you show up on race day you are not fumbling around trying to figure something out. Nothing worse than finding out your headlamp bounces around too much and your running vest does not fit the way you expected it too.
Another benefit of running with your race gear regularly is you learn about it. What pockets work for what. How long batteries will last in your headlamp. How much water is comfortable to carry. How the gear works. While out on my run yesterday I went to take a drink from my hydration pack and no water was coming out. I was like WTF!!! So I had to stop and investigate. I removed the hydration pack from my vest and everything looked right. I was like crap I am going to need to cut my run short. No way I was going to run for two hours in 85-degree weather with no water. After some quick thinking, I figured out the issue. The connector where the tube connects to the bladder had popped out of its seat. So it looked fine but the seal was not made and not allowing water to pass through the tube. I popped it out and reset it. Finally, the water was flowing.
So what did I learn by running with my gear? I now know if the water is not flowing from the tube in my hydration pack I need to check the connector. I stressed for a few short minutes yesterday since I wanted to get my run in, but now on race day if this happens there will be no stress. Just a quick easy fix.