Ultralight backpacking is a philosophy that gear functions should be the lightest practical weight.
For example, if you want a lantern for diffusive lighting at camp, you can use an inflated balloon affixed to your flashlight or headlamp, saving the weight required for of an additional light. While having more than one light is a good idea, weight can be saved overall by a less powerful and less heavy secondary light, especially when caving (spelunking) where loss of light can be life threatening.
Because the functions required are expedition specific, the gear choices you make will vary depending on the trip.
The gear choices will also vary depending on personal preference. While I don't consider a camp chair essential, others might. In some unknown case, depending on the trip objective, I may want a camp chair, and I would find a lightweight option to carry with me. My default is a foam sit pad that costs less than $3 and hardly weighs anything.
For really cool gear, check out Etsy with search terms like “ultralight backpacking”.
Select your topic of interest:
Google has become an evil capitalist empire, serving corporate profits rather than returning good search results. So I am assembling a list of ultralight backpacking forums where I think you may find non-marketing answers to your questions:
Everything you need in the following kit: Adventure Medical Ultralight / Watertight .3 Medical Kit Except for loperamide, an antidiarrheal.
What you may not want, is an antibiotic ointment: