what would you suggest we place in it?

Might as well stick one of the front desk people in there, too. Virtual key sent to your smart phone and straight to your room.

....unsealed, of course.

A pill of your ED medication of choice.
In the future I'm quite sure guys will have bionic penises.

Versatile.  'ludes or crack.

A Qualude dispenser should have Bill Cosby's name on it.

....a toothbrush, strong minty toothpaste and any of the other 47 things we all use to make sure he/she really wants to kiss us....

from a certain now-defunct web site. Afterall said web site used to be the equivalent of the Roman Empire for P4P in its glory days!

such as the Village Voice in NYC, where, prior to the existence of the Internet, we found ads for providers and massage parlors.

preserved body. When I am reanimated in 2085 I will dedicate all further conquests in the hobby to the items you included in said capsule.

A hobbyist guidebook to not getting robbed or bait and switch, add in a good porn so hobbyist can recover from the stories in the handbook.

With instructions.  

someone in the future will get a great laugh as we did

I'll do the pouring.

..as simple as an escort’s autograph on a napkin, or some object of hers (like her lipstick), of course agreed upon to take; then a written review attached.

Sort of an Aida thing, if you recall that ending

displayed on the bed--including, perhaps, the lovely lady since by the time it's opened, who cares?

For the clean up after........

Gillette or other brands

but I too remember keeping a supply of "weed and ludes" strictly for female company back in the 80's living in Vegas. I had already pretty much quit smoking pot by then and I never much cared for any kind of downer, but the ladies liked them so I kept a small stash just for them.