A wifi card - PC Card or USB - is obviously essential.
I would think that for that length of time you would be better off looking for standard wifi hotspots rather than 3G.
You can use a mix of either free (e.g. McDonalds), paid on the spot (e.g. Hotels, Wetherspoons, voucher-per-drink) or using a roaming payg account like Freedom4 (previously known as BOZII) or BT Openzone.
SD