I assume you already know how to access the internet with the Touch, using Wi-Fi, or do you?. If you have a wireless router, your Touch can connect to the internet through the router. This is the only way the Touch can access the internet. So the only way I know to use the internet while away from home is to access a free Wi-Fi network.
In some countries, certain coffee houses (shops) have free Wi-Fi that the public can use, but it's not that simple. Here in the UK, I know of two pubs that allow me to use their Wi-Fi, as I'm a customer. But one of them wants my email address, which I don't want to give them, so I cannot actually use their Wi-Fi.
So access to the internet via the Wi-Fi would depend where you are going on holiday. Does the train service you intend to use have Wi-Fi facilities?
ADSL is a wired connection, so you would still need to connect a wireless router to the ADSL connection for the Touch to connect to the internet and arranging this for a holiday is not practical.
Prepaid card for what, access to Wi-Fi? The UK doesn't have such a network, as far as I know (and I live here) so if your holiday is in the UK, that idea will not work.
The reason you've found lots of into for the iPhone is that it is a phone and it uses the phone functions to access the internet. The Touch cannot do this.
Phil
P.S. Now that I've said my bit, you can be certain someone else will come up with a "supposed solution" for you!