I was just sorting out ultralight gear for the summer season.
Boy, it seems like choosing how ultralite to ultralite involves significant volume considerations that come into play when choosing "how ultralite to ultralite" it.
The comparison between ultralight kits was highlighted when I looked at several of my shelter options-
an UL tent - 1kg
an UL tent/tarp combo - most roomy and airy, very close to the same weight, 1 kg.
or a superultralite -SUL - option - a 5x8 tarp and a mosquito headnet - 9 oz.
Three different tents, three different volumes of gear to pack. With high mosquito season soon here, one of the two heavier options is more appealing. The downside is they compress considerably larger, about three times the volume the SUL tarp. Going with saddlebag like a medium sized Carradice seems to necessitate carrying the shelter outside the bag unless packing super ultralite.
Sometimes you want to bring spare shoes like crocs or rollable shoes for down time off the bike. A second pair of bike shorts are almost a necessity on longer trips, unless you decide to ride in non bike shorts while riding on wash days. A rainjacket is an absolute must unless are out on a short trip with no chance of precip, or don't mind getting wet if it begins to pour.
Warm clothes for nightime, hat, windshirt, second pair of socks..... it all adds up in volume.
UL packing is a real study in reductionism and savvy packing.