A laptop with a 802.11b/g would be sufficient. No additional equipment is required to connect to public wifi hotspots. As you say some are free but others require a paid subscription. This link is helpful at locating hotspots worldwide click here
Bluetooth tends to be used mainly for connectiong mobile devices, mobile phones etc. Ethernet tends to come as standard on laptops these days but would only be required if you intend to WIRE the laptop to a network rather than WIRELESS.
I have recently bought a Centrino laptop which has built in wireless but is also lightweight and has a good battery life, around 5 hours, which is ideal for travelling.