Strange women lying in ponds distributing swords as a basis for a system of government.

Guillotines.

Having most of the year off for festivals and holy days

My non-joke answer is apprenticeship. Kids could actually learn how to do a valuable job rather than graduating from high school with almost no useful skills.

Royal beheadings

Our leaders fighting in the wars they start.

You wanted it... go fucking get it cowards.

Guillotines obviously.

Regicide.

Peasant uprisings, to take down the kings of today.

Beheading kings.

Cloaks would be cool. I know that's more of a fantasy aesthetic than a medieval one but they are cool enough that it shouldn't matter.

Inns, especially if they've got an enormous pot of perpetual stew, and people are giving out quests.

Catapults, just to irritate the trebuchet people.

Guillotines for kings

The stockade is something we desperately need. Some people need to learn how other people see them. Driving 50mph in a living area, stockade. Making a lot of noise at 6 in the morning, believe it or not, stockade. Being a racist cunt, straight to the stockade.

Trebuchets - the superior siege engine. (Disclaimer: probably not medieval)

Cloaks and leather boots

Dueling. I say we use it as an option to reply to a civil lawsuit. Able bodied adults only, no proxies, and if you refuse then you have to do a trial and they can weigh your refusal as evidence against you.

Swords only, no guns.

Royalty and nobility taking part in actual on-the-ground warfare. I'd be curious if that would have any effect on military operations...

Receiving land for farting good.

Mandatory longbow training for yoemen and yoewomen. Let's get those skills trained up in case we're ever facing a charge of French knights.

Fucking guillotines already

Sorcery, alchemy, soothsaying, baby. Come one come all I'll cure what ails you. I'll summon portals and turn lead into #gold.

Or maybe the town crier. Hear ye, hear ye, elon musk hast tweeted about his balls.

I guess we could use a little ice age right around now, and it would also be nice to have a Renaissance around the corner.

Someone said inns and taverns, and yes it's a missing piece of housing here - long term hotels with food, bars/restaurants with rooms to rent above.

Not much though, it is not a time I'd visit.

Weird ass slices in public parks everybody has to garden in. https://en.m.wikipedia.org/wiki/Open-field_system

Random pedestals with swords driven into them lol

Kings, plagues, private armies (more late medieval and renaissance, but you get the idea), career military with hi-tech weapons tearing apart barely armed peasants. Idk, OP, seems like we got almost everything covered

Bathhouses. The local Quicklee's just doesn't do it.