I love this idea so much that I might adopt it: if a PC creates a new spell/magic item/secret technique, etc., it probably SHOULD have the PC's name in it!
Here are some ideas for non-caster legacies:
1. Magic items. Allow anyone with proficiency in the proper tools, and who has the magic item formula, to craft magic items. E.g., if you are a dwarven blacksmith, then you know mundane smithing techniques AND magical ones. When the formula for a flame tongue says to forge an iron sword blade decorated with rubies and wrapped around a red dragon's tongue using a forge fueled by a fire elemental, you know how to do all that stuff.
If it makes you feel better, you could limit this to characters with the Ritual Caster or Magic Initiate feats. Or you could create a custom feat for it; but feats are expensive, so the feat would need to provide substantial benefits beyond the ability to blow cash and downtime on crafting. Or you could give casters some other edge over non-casters, like maybe a non-caster pays more money or has to be a higher level than an equivalent spellcaster.
2. Secret Technique Feats. Creating "generic" feats doesn't sit well with me. Feats are expensive and may be unbalanced. Implying that there's a "Rapid Shot" feat that lets you shoot a bow as a bonus action changes some things about the setting and how archers operate.
But if it's a Secret Technique -- "Lyllandra's Extra Arrow Technique" -- that your character develops over time, that's different. Only people the PC teaches will be allowed to take the feat. If it's overpowered, then it turns out that most other characters just can't learn it (or don't want to) and the Secret Technique dies with the PC. This lets you sort of have-your-cake-and-eat-it-too regarding experimental, player-created feats.
3. Laws. Or rules, precedents, or guidelines. These might be invented by a PC, or discovered by them. The Code of Hammurabi. Newton's Laws of Motion. The Peter Principle. The Brady Bill. Miranda Rights. The Streisand Effect. So it doesn't have to be a law the PC creates willingly, or even knowingly.
4. Landmarks. It's extremely common to name areas or landmarks after a person who discovered them, first settled them, performed a great deed near them, etc. If your campaign features a lot of wilderness exploration or colonization, the PCs could easily wind up on the map.
5. Ballads. This one is my favorite. Minstrels and troubadours throughout the land sing of your PC's heroic deeds! Or sing embarrassing diddies about your personal flaws. Either way you get to be an object lesson for future generations! Plus, this is something that can come up a lot later in the game or in future campaigns. "You all meet in a tavern, where the bard is performing The Ballad of Vulknar Stormreaver, a half-orc with humble beginnings who grew into a mighty warrior and eventually defeated the evil elemental prince Imix by dousing him in mayonnaise from an alchemy jug..."