Those caps Kyle linked are inexpensive and work pretty well unless the pipe gets tossed around aggressively (liked knocked against things or dropped). I live on the ocean and the wind caps are also great when smoking outside on windy days.
The caps work with most pipe bowls, but if you looking for a new travel pipe, I'd recommend something short and sturdy such as these:
http://pipesandcigars.com/salopi.htmlThere's also similar pipes and "nose warmers" in similar styles at higher and lower prices.
Savinelli also makes a relatively short and sturdy "Author" -- the 320 shape that might be suitable.
A MM corn cob might the the WTG -- if it breaks or it's lost it's more expendable.