I would say that I can now live a good month out of a 30l backpack, even though I have a DSLR camera equipment with gimbal and a notebook with me. That alone accounts for most of the weight and fullumen. That’s why I’ve made it my challenge that at least the rest needs as little space and weight as possible.
I want to show exemplary how a composition for a 4 day trip looks like.
I use a 4g PVC pressure seal bag as a toilet bag. With such plastic bags I separate hygiene articles from clothes and technology. In the past I used to use one pack of Cube for each. But a single Medium Packing Cube (Amazon Basic) alone already weighs 60g.
Toothpaste tubes are bulky and heavy. Either you always have to buy travel tubes or take an opened tube with incalculable residual contents. Avoiding heavy liquids when travelling is not a bad idea.
I now use toothpaste tablets in everyday life and when travelling, which I can dose exactly to the day. A daily dose of 2 pcs. weighs 0.6g. The tablets can be carried in small PVC bags (0.7g) to save space.
As toothbrush I use a classic model with interchangeable heads. The thing is light and the style is not too long.
I can also take cotton / bamboo cotton swabs with me counted. One piece weighs 0,25g
I pour deodorant into a small plastic spray bottle. The empty bottle weighs 10g. For a daily ration of deodorant I calculate with 1g. I would prefer a powder solution because I could get rid of the heavy container and I would have to carry less liquids. But I have not yet been able to gain any experience here.
I always travel with a double set of clothes in my backpack. One pair I have on, the other one is in my backpack. During the day or at night my clothes dry in the accommodation. For washing I use 3g of this wool detergent per day in a 7g plastic tube.
The toilet bag for the 4 days weighs 52g and takes up practically no space in the rucksack.
Once you have figured out how much of each object you need per day, you can scale almost all articles to suit your travel time.
For even more info I can recommend /r/onebag and /r/ultralight Subreddit. This is where people who want maximum functionality or maximum weight savings when traveling exchange ideas.