Agree with this. I have built a web site that allows drawing using the HTML5 canvas and it works fine. You would need to store persistent data somewhere but the
drawing is very easy and you can generate a PNG file from the canvas trivially.

This works with Firefox, Chrome and Opera on Windows and Linux. It won't work with IE7 and earlier (I haven't tried IE8 but I doubt it). It should work with Safari but I haven't tried it.

If interested, I can post links to good tutorials (but any reputable search engine should find them).

It is relatively easy to travel with a laptop but you may get tired of carrying the weight around.

You won't need a new power cord - just buy a standard power adapter - cheap and small and can be used to charge other kit.

The benefits of having your own laptop are that you can easily store photos and if you connect to WiFi (I am not aware of regional variations) you can do email etc. You can get WiFi either from coffee shops or from your hotel but it will not be free.

However, when I travel with a laptop, I do get sick of lugging it around. It is relatively heavy and bulky but is too valuable (read worth stealing) to leave lying around. If you can leave it in your hotel room then it should be safe. If you are using hostels etc. then that may not be the case.

If you can live without guaranteed Internet access and have ways of saving photos then leave it at home.

While you are in London, I strongly suggest visiting the Natural History Museum. IMO this is one of the best museums in England.