"What do you have in your hands right now?"
(This is only mildly related to the "What's in your mouth?" question I'm always asking my dog on walks.*)
Everything a PC does is influenced by the answer to this question. A PC who isn't carrying a light source in a dark room won't be able to see--something the GM should know before they ever give their scene setting description. Anything a PC attempts might be hampered or helped by the answer.
Player: Can I climb the wall here and look over it?
GM: Well, the wall is made of crumbling brick, so sure, it would be easy. What are you carrying?
Player: I'll leave my sword and shield on the ground.
GM: OK. So you prop your sword and shield against the wall and start climbing the wall?
Example the Second:
Player: OK, I want to try and pick the lock on the weird door with the face.
GM: Who has the light source? (A variation on "What's in your hands?")
Player 2: I do. I'm standing guard by the first room to make sure nobody ambushes us.
GM: If you're trying to pick the lock but your light source is at the cavern's opening, you basically can't see what you're doing. That'll be a massive penalty.
Player 3: I'll pull out my torch and light it off of Player 2's and stand near the locked door to provide light.
GM: OK, that works. Make a Pick Locks roll.
Example the Third:
GM: You see a bunch of little cube-shaped cuties walking in a line through the forest. The last one in line notices you, exclaims in surprise, and then hurries to catch up with the rest.
Player: I want to catch one!
GM: Do you have a free hand?
Player: Uh, no. No I have my sling in one hand and my shield in the other.
GM: OK. How are you trying to catch one?
Player: I want to put my shield down in front of it. Like, reach over it and try and trap it between me and the shield.
The fiction of what a PC holds gives you immediate context for the rest of the scene.
* Spoiler alert: It's poop.