Just another "yay!" for Xarchiver from over here :P. When not using the hefty PeaZip, it's pretty much always Xarchiver for me. It just seems to sit so well within the Fluxbox aesthetic.
On the topic of file management in Fluxbox, I hope you don't mind if I add a seemingly random mention of an obscure file tool here. It's not like a packaged, repo-available app, and it's just that its vibe is like the custom Fluxbox goodies included in mxfb. I have a feeling it integrates really nicely with rofi and the like, and potentially a great little touch to include as a default.
So, yeah, lately (a couple of months), I've been using a peculiar little utility more and more, and it really feels like it complements my Fluxbox experience

... I use the terminal a lot, and do file operations that involve fuzzy searching, you know, fzf, ripgrep-all, ugrep type of stuff. Sometimes it feels like: man, okay I've got these results here, I'd actually like to trivially keep them around on the desktop and potentially open these and these files (from many different directories) in these and these
GUI applications, just like that. If there just was a... file palette of some kind, a drag&drop sink that I could... pipe these results to, and it would then show these files neatly and they would sit there until I close the window. Clickable and draggable. A bridge between the terminal and the GUI world, temporary ad hoc file bookmarks, kinda.
Turns out, as I actually googled it, someone coded just that a few years ago. I decided to try building it (upped the maximum file number for a particular mode somewhat) and it's just great imo.
https://github.com/mwh/dragon
Video demo of the basic functionality (there's some more polish in it these days)
https://www.youtube.com/watch?v=ukIG_OVXa3Q
Sorry about blabbering about that, I just figured I had to mention it in case someone goes as bananas about it as I did, hahh, and goes for a rofi implementation or something. It feels
so mxfb in use and blends in, in daily tasks.
I promise I won't flood about it more than that; just had to mention :')