Sure.
Something like the AD&D 2nd edition Complete Fighter's Handbook, or more importantly what it aspired to do. Like, if you wanted to play a bronze- or stone-age campaign, not just how to do it, but how to do it but still fight dragons and ghosts and such. Same with a sea-faring campaign (preferably not just 'everyone play a dex-based fighter') or swashbuckling (fighter) campaign.
Likewise, more things for fighters other than more character-build options to take. New actions or maneuvers any fighter can do. More actions other than combat -- the 2e one spent time on smithing, this could be leadership or mercenary companies or mini siege rules. Downtime or reputation rules, dueling rules.
Mundane item rules more complex than what we have. Maybe an armor list for people who hate studded leather and ring mail and other historical inaccuracies. Different arrow types. Martial spears. Maybe a 'fantastical fantasy' subsection with stuff like D&D 3e had (thunderstones, tanglefoot bags, spiked chains and dual sided weapons). Rules for minor upscale enhancements for campaigns without magic items (or in addition to) -- hidden compartments, poison reservoirs, push-button holy water sprayer, who knows.
Mostly just more stuff other than new sub-class and feat options.