If it's your first time going for a couple weeks on a trail with just your backpack, you may found it difficult to know what to bring with you.
One rule is only the strict necessary ! As light as possible.
We often bring things that we believe will be of use but once we spend the entire day walking, we figure out that even if we arrive early at the refuge for the night, we are often too tired to do anything else than eating, resting, and journaling.
But don't worry if you packed a few stuff that appears to be unnecessary in your journey, it's a classic. After one or two of walking, a lot of pilgrims -including myself- are stopping at a post office to send back home those unnecessary things that make the bag heavier.
The golden rule is that your backpack should stay around 10% of your weight and can't in any case exceed 15% of your weight.
Keep in mind that you're going to walk a couple weeks, and that even if you're use to 2-3 trails in the mountains, the long time effect of your equipment on your knees and ankles can make a all difference on how your trip can turn into a painful mission or a fun adventure that will most likely want to extend.
The most important thing where you can save weight is your backpack. (Here is a list of recommandation of backpacks, my personal favorite one is the Osprey Levity 60 who's weight is 900 grammes).
So my recommendation is :
Keep in mind that when you think that one element won't make the difference, it's the total amount of those elements who will start to make your backpack feels heavy. In one month I have walked over 1.2 million steps, so a difference of 2kg would be a total of 2.500 tons less on your knees and ankles.