congrats with your new laptop
IMHO it all depends what you exactly want to do with it, create some loops and stuff that you can use later on your Main DAW, or actually play some melodies ? I'm doing a lot travelling myself and have allways my laptop with me, but I wouldn't travel with some keyboard. Problem is that you have to carry it... if you only travel by car that wouldn't be a problem but I also travel a lot by plain and there the situation is different.
If you want to go that way, I have the M-AUDIO OZONE since a couple of years now and I must say that it is a good keyboard and the controllers are of good quality (no problems yet) but it suffers from a flaky USB driver, the driver works good but it takes way to much CPU. I have read a couple of test of the X-station and it seems that this one is still pretty buggy.
Comming back to your question, I wouldn't go for an external soundmodule if you just want to play a bit with FLS when your away. As long as you're staying in the digital playback domain, your internal soundcard would do (AC97 card?). IMHO an external soundmodule would only be justified if you want to do some recordings.
If you need a keyboard ? That's up to you to decide
Kara