comments:
Similar problem: My current under-saddle bag is almost exactly 1 L (measured with a water-filled quart ziploc bag, at 0.96 kg = 0.96 L; the exterior dimensions given multiply to 1.7 L, but it's not really rectangular), and is stuffed to the gills with a standard spare tube protected by double layer nitrile gloves, tire levers, multi-wrench bike tool, foldable pliers/knife multi-tool, patch kit box, and a small microfiber cloth. I carry a pump on the down tube. I'd like to fit a rain jacket (ziploc 'vacuum'ed if necessary), some chain tools, and maybe a power bank. I'm going to try the REI 3 L 'junction seat bag'. Hopefully it won't obstruct the rear facing radar light. An expandable 1.5L/2L under seat bag might also work, but after litering out my current bag I'm a bit wary of going by listing information.