I did a two week kayaking trip a couple months ago. After two days when I was stuck on shore due to big waves with little to do, it occurred to me that I had not weighed my food for the trip. I had my luggage scale with me which allowed me to weigh my four dry bags that were mostly full of food. After I had been eating for two days, I still had 15 kg of food (plus the empty weight of four dry bags) remaining.
I know that there are people that get enjoyment about drilling holes in their toothbrush handle to make it lighter, and for those people all I can say is that am quite happy that you have found a way to enjoy life. But, that is not for me, I find it quite difficult to get excited about cutting down the weight equivalent of a quarter of a glass of wine.
Your plastic bolts, they do not need to be tightened very much, you should not worry about shearing off the heads. In some places they will keep water ingress from your frame or fork, thus lightening your load by a few ml of water on a rainy day. I will continue to use stainless bolts in such places.
I agree with Dans comment on a water bottle, if I had to use my last water bottle on my bike I consider that to be running low on water for that day of travel. I like to finish the day of riding with one full water bottle for safety purposes, and since I use one liter bottles for touring that is one kg of water that try to carry without using every day.