There are a couple of ways of acheiving this:

Adhoc, peer to peer, computer to computer

You can create a peer to peer wireless network between devices that does not require an Access point or other routing device. This is usually known as creating an ad-hoc wireless network, or a computer to computer one, rather than an infrastructure one.

I currently only have access to a machine with Mountain Lion on, and things appear different (this method is unavailable), but in Lion or earlier you should be able to:

1. Go to the menu bar, go to your network indicator and choose "Create Network..."
2. Enter a network name, and security settings if required
3. On your iPad, go to Settings, go to WIFI and choose the network you just created. Enter the password if you set one and you should get connected.

Any devices connected this network should only be able to communicate with other devices on the network, no routing or other traffic is available.

Internet Sharing

Another option is to use Internet Sharing. On the off chance that you have free or cheap hotel internet:

1. Open System Preferences and go to the Sharing pane under the Internet & Network heading.
2. On the list of services to the left, select Internet Sharing. Don’t check it quite yet — there’s a few options that need to be set first.
3. Depending on what your current internet source is, select it from the menu next to “Share your connection from.”. Built-in Ethernet is a good choice, but if you have a mobile broadband dongle you could select that also.
4. In the “To computers using” box, select and check AirPort/Wifi from the list.
5. Click on the AirPort/wifi Options button to configure security settings if you want any.
6. In the window that pops up, type a basic Network Name, Click OK. Setting up Mac OS X Internet Sharing
7. The configuration portion is finished, so the only thing left to do is check the box next to Internet Sharing and enable it. A confirmation message will appear — click Start to complete the process.
8. Now that your Mac’s internet is being transmitted from your AirPort WiFi card to other devices, you should see an different icon in your menu bar. If you do, you’re in business!
9. On your iPad, go to Settings, go to WIFI and choose the network you just created. Enter the password if you set one and you should get connected.

Now any machine connected to the same wifi network can route through the ethernet or dongle connection on the air. If you have no connection available through those connection, then the same peer to peer communications should be available still.

If your Router has two different antennas sending on different frequencies, see if your iPhone uses a different one as your Air, and if so, try to connect to the other one.