1. Use a USB dongle
Using a USB dongle to provide Internet access to a laptop maybe getting a little outdate as you can only connect it to your laptop restricting its usefulness, however they can be bought very cheap and for occasional use they provide good bang for your buck. Many offers online include preloaded data and can be had for as little as £30.
2. Tether your phone
Tethering to your phone largely depends on what mobile provider you are with and which plan. Many cheaper plans do not allow tethering at all, but you can sometimes get away with brief use. Tethering with Android is a lot easier than with the iPhone as these can sometimes have the tethering feature locked down.
The obvious advantage with tethering is being able to have 1 contract and 1 device for all your mobile needs, but tether is a massive drain on your battery and if you are a heavy user it may be wise to use a dedicated device.
3. Use a portable WIFI device / MIFI
MIFI devices has largely superseded USB dongles, many of these devices will allow 5+ devices to access the internet simultaneously. Newer models are also 4G speed meaning you can often get faster than ADSL speeds while away from home. The downside is that they can be expensive initially to buy with 4G models often costing in excess of £100 sim free. You can get them reduced if you commit to a mobile contract but this is not ideal for the occasion user. If you are travelling you can get internet on the go in Europe by renting a device and services like these are becoming more popular around the world.
4. Access free or paid WIFI service
In the UK there are many free hotspots, and many more paid hotspots that will allow you to work while on the move. If you are an O2 or Sky user you can access The Cloud for free which is available in many cafes, restaurants, pubs and shops. Alternatively if you are with BT they have their own hotspots that you can access.