Usually wear chinos or work pants with my flight jackets, if jeans are old high-waisted Levi 505s ( US made ) or old good 501s or Lee 101 from their archival series from the 1950s.
However, my absolute favorite to go with A2/B15 is the randomly purchased limited edition made of Kaihara raw denim jeans from Japanese Uniqlo U-series. Wide fit in the spirit of 40s work pants, high-waisted, very smart look, large back pockets and a great fade after years. I bought 2 pairs 4 years ago, one is pretty worn out, second I keep as a reserve. If I have time later I'll add a pics.