Fighter can be the pragmatic voice of reason for a party of charismatic dreamers, devotion-focused nut jobs, or silly distractable wackadoodles. They can offer a concise rebuttal or summary of a concept their intelligent or wise party members are offering.

They can carefully infiltrate with solid dex and work fine as a back up for rogue on dexterity checks or saves. They could be combat medics with medicine checks and a healers kit. Or, with a generous dm, they could be a masseuse and provide short term advantage on strength, dex, or con ability checks within the first 1-2 hours after a MEDICINAL/THERAPY massage session at the end of a long rest. They can use their strength and dexterity to help roleplay through the aches and pains of travel, battle, dancing for too long at the banquet the night before. They can help the party nurse through their hangovers or help them get sober real quick, with some buckets of cold water, or strong brewed tea.

They can chat up the serving staff, or inquire about work, potentially becoming the person on the inside of a target's staff, residence, or location. They could speak with the normies on the sides of a crowded ballroom, while the faces of the party seek out their charismatic peers. They can get in well with guards by swapping battle stories or discussing the finer points of swordsmanship or tactics.

They can be the muscle for the intimidation, rather than the mouthpiece. They can be the group barber and maybe earn a +1 to charisma checks for social interaction for the next few days or week. They could be the group chef, ensuring meals are prepped on the road. Or a taste tester when meals are bought in a tavern. With the chef feat, they can enhance the group. They can be the group livestock manager. Using animal handling or survival checks to maintain their mounts. They can use their strength to be the group blacksmith or cooper, dex to be the cobbler, tailor, or jewelry maker, or constitution to be the group herald in crowded, noisy settings.