Girls understand that you live in a home, and not a hotel: there are certain amenities which they do not expect to find while unexpectedly crashing at your place. (For instance: a hair tie.)
That having been said, there are a few things that a girl would hope to find while spending the night with an adult.
1. Clean Sheets
Clean. As in, have been changed recently. Not lint-rolled. Changed and washed.
2. TWO Towels
Girls like two towels: one for their body and one for their hair.
3. T-Shirts Of The Right Sizes
You should absolutely offer a girl something to sleep in — whether she’ll take you up on it or prefer to sleep naked is a matter of personal preference, but better to ask than not.
If she does want something to sleep in, boxers and a tshirt are fine, or even just a tshirt. The t-shirt should be BIG though, as big as you have.
In some situations, you might offer her something to wear the next day, either home or to work. For this, go for the smallest shirt you have — a white button-up will almost always work, or a simple t-shirt. She might ask for a belt.
A polite girl won’t steal your clothing, but if you’re worried about getting your stuff back, give her a shirt you don’t normally wear, just in case.
4. Shampoo AND Conditioner
Girls hate stepping into a guy’s shower to be faced with nothing but a half-used bottle of Head and Shoulders shampoo. Conditioner is a vital part of most girls’ shower process, and, bonus, can be used as a makeshift shaving cream (if you also happen to have an extra disposable razor on hand). You can always take the extra bottles from any hotel stays, collect them together, and let her choose what she wants.
5. A Robe
This needs clarification: you shouldn’t have a special robe that you clearly reserve for your overnight guests — girls will immediately see through this and be totally skeeved out. But a robe, whether it’s yours or a random extra one you have, is essential, especially if you have roommates that she won’t necessarily want to meet while sneaking to the bathroom in whatever state of undress.
Bonus Points For: A hair dryer, an extra toothbrush, face wash, coffee maker, good cereal, ice cubes, an umbrella, enough blankets, asprin or motrin, extra contacts solution.