TP-LINK TL-WR802N N300 Wireless N Nano Router - $14.99 AC + FS

Would this let two devices (e.g., 2 smartphones) share one wifi connection on a plane?

Quote from swooper : Would this let two devices (e.g., 2 smartphones) share one wifi connection on a plane?

You're looking for 'Hotspot Router Mode', which this device is supposed to include.
I use a similar device (with built-in battery) to do the same.
This device will connect to the hotel/airplane wifi, and your phones/tablets/laptops connect to this device's wifi.
Hotel/plane sees only one device connected, so no additional charge

Quote from swooper : Would this let two devices (e.g., 2 smartphones) share one wifi connection on a plane?

Yes, but not the greatest experience. The Ravpower & HooToo FileHub products from Amazon (same company) will do it better. They an app which make configuring them for hotspot access on the fly (no pun intended) really easy and will do network media streaming from their USB/flash memory slots and also have built-in batteries for running the device itself and charging phones.

I already have this TP link but bought the RavPower FileHub Plus because of the better features/accessibility while traveling.

Also if you have a recent Samsung Galaxy phone you can just use the built-in wireless sharing feature to share with other devices (up to 5, I think).

Quote from swooper : Would this let two devices (e.g., 2 smartphones) share one wifi connection on a plane?

This is a travel router that allows you to share a wired or wireless connection and behind a firewall. However, this one does not have battery built-in, so you need to provide a USB power source to it. I have two travel routers by Ravpower that have battery inside but still in a similar size like this. In addition, one of them is dual band. It is particularly good when you are travelling with family or have multiple devices to be connected. I have used it on a cruise, Starbucks, and in hotels. I only need to connect on one device through the router and all other devices will be connected and in a private network.