I think having the guest bedroom 100% ready to go would be toward the bottom of my list. Most often, drop-in type guests aren't going to end up spending the night. If they do, it doesn't seem terribly important that the room be ready for them without 20 minutes of fussing around.
In addition to biscuits, I'd also always have something like a bag of tortilla chips and salsa, or Chex Mix, or something along those lines. Unless you have reason to think you are going to have lots of drop-in overnight guests, I'd worry more about what to do to feed and occupy people for 2-4 hours. Shelf stable snacks, cards and/or board games, etc. Coffee and tea (as well as the additives), even if you don't drink them, and perhaps even a few cans of soda. I also always have at least 2 bottles of red wine and a bottle of white in the house. I can pop them open for guests, and they also make good last minutes gifts if I have to run somewhere.
That said, I basket for your guest bedroom with toiletries (take the ones from your next hotel stay), a WiFi plug and cable, a few small snacks and a couple bottles of water, etc. is always a nice touch for overnight guests. If you want to be fancy, a robe and slippers in the closet is a nice luxury.
Beyond supplies, generally if your house is kept to a decently clean standard, you'll be fine. Guest don't care that the lamp shade is dusty, or even if there is a dust bunny in the corner.