Phone tethering makes it really easy; I'm having a lot of fun spending my afternoons coding in the park. Otherwise, if you're away from any connectivity and you're working on something local, I highly recommend the Stack Exchange data dump[1] along with Samuel Lai's excellent Stackdump[2]. I worked without internet for 2 weeks using this setup (+ offline documentation) with great success. (Warning: Stackdump copies the SE XML data into a local database, which currently takes 7 hours on my Haswell i7 and requires extra disk space. Prepare ahead of time!)
[1]: https://archive.org/details/stackexchange
[2]: http://stackapps.com/questions/3610/stackdump-an-offline-bro...