There are some popular houserules, like handwaving Ammo and carrying capacity,
VTTs and digital character sheets make this trivial to track, so I enforce them. When I was playing in person with pen and paper, I just applied a loose reasonableness test.
that the D&D community kinda assumes is common enough that if you were to walk into a random table, you could expect not to run the rules RAW.
I don't walk to any random table with expectations regarding house rules. There is too much variability among DMs. The only situation where I think expecting game to be run RAW is in organized play games like Adventurer's League.
What are those houserules and what do you think about the idea of houserules so common that you don't even ask your DM/tell your players about it?
For me, personally, none. As a DM I clearly lay out the campaign world and any home rules, reserving the right to adjudicate on the fly. I've been playing with the same group for years and we generally decide on the campaign and house rules by consensus.
When joining another groups campaign or playing in a convention game, I roll with whatever the DM decides.
In my experience the house rules that most players prefer, if not expect, is a certain amount of hand waiving on encumberance, ammo, and spell components. I large number of players just detest granular resource management.
Regarding components in general, this is a case-by-case home rule situation for me. I generally try to support the players' character concepts. I have no issue with weapons or shields being treated as foci and that the movement of the weapon or shield being treated as somatic components of the spell. Its cool, make in-world sense (to me), and of all things that get me concerned about balance, this is gives me no concerns. The one exception is verbal components. It is difficult to cast spells with verbal components without other noticing. I want things like Sorcerer's subtle casting to mean something. I might allow players to make a deception or performance check while casting spells when they don't want others to detect that their characters are doing so, but it is very situation specific.
I have a campaign on the back burner that would be a wizard focused campaign in a low magic setting where I would not allow magic foci and material components would be tracked and be a big part of the quest lines. But my current group of players aren't interested in it. In an old post in EN World a few years ago I was actually accused of being a bad DM for thinking about enforcing that (as well is limiting character and race options).
It seems most of the players I have interacted with REALLY hate having to track or even think about spell components. I have to find those folks who spend hours collecting herbs, fungus, and butterflies in Skyrim. I can't be the only one, right?
I house rule light mostly for my own sanity because it is a pet peeve of mine how torches are depicted in games and media. Since I've moved to a VTT, however, vision and lighting have come back to being played pretty much RAW as the software takes care of it and has cool graphic effects when you are using dark vision versus lighting. I've long escaped the verisimilitude trap and am no longer a jerk about torch smoke, time for eyes to adjust to darkness, etc. During times when I run things by theater of the mind, I just fudge and describe things in a way that feels right.