Do you need a full base layer and camp clothes?

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Since the word "ultralight" is used in the first sentence, I'll throw in this advice. Every piece of clothing you carry should be able to be worn at the same time, as part of a coordinated layering system. This doesn't necessarily negate the "two sets of clothing" concept though. If your "sleep clothing" is a base layer of a jersey and long johns which you may or may not need when hiking, you're complying with the idea. You'll do that for the first month of an AT NOBO hike, for instance. In the summer, you may ship that layer home because you don't need that "sleep clothing" any more. As many others have said, it all depends on the season.

In another example of going ultralight, I no longer carry a puffy jacket "for camp" on a thru hike. A decent camp jacket not only weighs a couple of pounds, you need a larger pack for the volume. When you stop and camp, you have a sleeping bag or quilt to keep you very warm. It's very unusual to need to wear a heavy, puffy jacket while hiking, and if you do, you stand a chance of wetting out the insulation and making it useless. I have a couple of lighter layers that can be combined to replace a jacket, and are more flexible for most thru-hike conditions. And one can be sent home for a summer season.

Good points. I’d like to add that IMO, it’s good practice to sleep in clothing to protect sleeping bags from sweat and oil. UL is great...it’s what I strive for...but my gear is too expensive to replace on a regular basis.

In warm weather, I’ve found a lightweight pair of running shorts with mesh liner to be invaluable. They can be used for swimming, sleeping, or when your underwear is too filthy.