karen2205 | Mobile Internet

Not planning on doing anything about this for a few months, but if I were to want a device capable of accessing the internet from a train, what kind of device would I want/how much is such internet access likely to cost? I've a preference for a qwerty keyboard with keys as big as possible for ease of typing. Also have a preference for being able to install stuff on it ie. Firefox, XiRCON, PuTTY.

Edit - Laptop is a possibility, but my current one is too heavy to carry with me just for 'fun' - I take it with me when I know I have a use for it, but it's too heavy to throw in my bag when I'm going to London for a day.