I would provide if we had internet:
A USB charging station that accommodates iPad, android, etc. (under $20 USD)
We do provide and have gotten good feedback on:
Ambient noise machines. Not because we’re drowning out noises but because the Man Of The House can’t sleep without one. We started with just one, but have purchased 2 additional ones that are going out with us the next haul. ($20 each)
Crib or pack n play if you want to appeal to young families. I don’t think it’s been used yet, but I’ve gotten a lot of OOH, A FULL CRIB type reaction from some moms on Instagram and in person showing friends the listing, so it must be really appealing for families. (My full sized antique-style wooden crib, $50 used. Looks brand new in spite of being used by my stepsister’s 2 kids, I feel like I stole it; she was long done with it and it was only taking up storage space. Win/Win.)
(I’d like to add an antique style high chair but I haven’t come across the right one yet.)
An outlet cover in the hallway that has a motion-activated night light in it. Walking around in the dark in a strange house trying to find which one is the bathroom door is not a problem for our guests!