A trick from us dirtbag ultralight backpackers - weigh everything with a kitchen scale and track in lighterpack.com
Seriously though, 40 liter backpack is palatial for front-country travel once I'm in the mindset of taking only the minimum necessary items and taking advantage of multiple use items.
You mention multiple use - that’s huge too. Shaving grams everywhere can add up to half a pound if you’re newer. Choosing the lightest of multiple options (lightest base layers, lighter cup, lighter pot) adds up to savings.