I mentioned this on another thread, and realized I should bring it up here, too.
Kenzer Co.'s Goods and Gear: The Ultimate Adventurer's Guide lives up to its name. I honestly don't think there's a better equipment book for any iteration of the d20 System, as it has not only weapons and armor, but things like clothing, coinage, food, musical instruments, transportation services, etc. It's technically all set in their Tellene campaign setting, but if anything that makes it more grounded (and easy to reskin).
None of it, as I recall, is Open Game Content though, since they produced their stuff under license from WotC in the wake of their settlement over WotC reprinting Knights of the Dinner Table for the Dragon Magazine CD-ROM Archive, so take note of that.
I mention all of that because when you run a low-magic game, mundane gear becomes that much more important, and this is definitely a book that excels in that regard (and also, all of the musical instruments, despite being non-magical, have a special effect for bards who use them, which is very cool).