Camp pants option

Longjohns or tights.

Lots of varieties. What temperature range are you looking for?

If it's hot when I arrive at camp, I just stay in my hiking pants.

When/if it starts to cool off, I change into silk-weight long underwear bottoms, and add a pair of ultralight rain pants as a waterproof/wind proof layer. Then when I'm ready for bed I just peel off the rain pants, and I'm all set. If it's really cold I add my Western Mountaineering Flash pants as an insulating layer.

I usually don't hang out in camp on longer hikes and just dive into my sleeping bag, but for 'social backpacking trips' during cooler-cold weather, the army liner pants work well. Basically a quilt for your legs:
http://stores.alleghenywholesale.com/-strse-119/GENUINE-US-ARMY-Military/Detail.bok

I've seen for $10-$15 at local surplus stores. Try to buy the long as the regular length is fitted to wear with high combat boots.

They work well enough by themselves; if you can sew even better.

Forget the weight off hand as I am not at home, but considering the army liner jacket modified with a zipper makes a credible Montbell Thermwrap clone at 12 oz, I am going to say they are very reasonable in weight.

Otherwise, I just have long underwear.

Buy a pair of nurse/doctor scrubs. Light, cheap, and comfortable

I carry a pair of my unlined cold weather cycling tights with no chamois. They're warm, compact, light, dry quickly, and I already own them so there's no cost.

I hike in a kilt, so they're also easy on/off if the temps happen to drop during the day.

Az

They are around 3.5 oz and it keeps the funk off my bag…sleeping bag that is

This could be a scenario for zip-off pant legs.
Rain gear.

I have worn a shirt as pants before, one leg in each arm. Comedy.

It's all about ultralight. Lounge wear is out! If it is cold enough to need more than briefs and tee for sleeping, I would have some sort of long johns anyway and would sleep in those (and whatever else is needed to stay warm. I'm talking silkweight long johns too. If I'm not in my sleeping bag, I am wearing my hiking clothing. I wear convertibles in the summer and would add long johns and/or my rain pants to add warmth— but I would be adding a vest or long sleeve insulation top first. If my hiking pants were muddy or wet, I would change to long johns and rain shell while cleaning or drying them.

Remember, for good UL practice you want to be using all your gear. Hauling another change of clothing when you have insulation and rain shells is a no-no. Many won't bother with extra briefs or socks, let alone another change of clothing to wear in camp.

If I were going to pick comfortable clothing that makes for excellent sleep wear, Power Stretch fleece tops and bottoms are super cozy. I wouldn't be wearing them when actually
hiking unless it is REALLY cold weather. A Power Stretch hoodie is my favorite non-lofty mid-layer top. A Power Stretch long sleeve top and long johns would go over a pound and they aren't cheap– you can burn up $100 in a blink.

I thought it was going as light as your own comfort and safety levels dictates for a given type of trip?

For what I call social backpacking trips, there is usually more hanging out in camp. It would be a bit anti-social to hang out by myself. And I am sure as hell not going to bring my expensive down bag by the campfire. :)

When I am solo, I don't bring a stove, dive into my bag right away and hike all day. Little time is spent in camp. I pack 8lbs of gear (minus the camera gear. That varies, too!)

Different trips, different goals and, many times, different gear. One trip s light, another trip is UL.

Just as there is no such thing as the 'best' gear..there is sure as hell no such thing as what every trip is all about. :)

HYOH, BINGO, XYX, ABC is easy as 123,HMHDI….etc,etc.etc