What type of development do you do? Is there no possibility of running your app locally for testing?
If you have Visual Studio you ought to be able to just F5 and do testing even without the Internet, although obviously you won't be able to connect to your company's source depot.
Some stuff to look out for:
* You'll need to manually sync if you're going to be offline for a while. This gets more difficult the more out of sync your code gets.
* Hopefully your company has the policy that all code in SVN must build, otherwise you will have problems if someone else on your team broke your code by submitting buggy stuff to the depot.
* You might need to ask your IT admin whether viewing source code on a train potentially opposite one of your competitors is allowed.
* You need to make sure that your laptop has Bitlocker installed, otherwise if you lose your laptop, you lose your company's secret source code.
Apart from that it should just work. There is of course the obvious problem that laptops are a little clunky for use on a bus; so you might prefer using either a very small laptop or a tablet instead.