I know it isn't quite as sexy as getting him a new tool itself, but if you come up empty, why not a gift card to the store in which he buys his tools, so he can select it himself, but you still get to buy it for him? I know gift cards aren't quite as exciting as the gift itself, but its an idea.
Other than that, don't know much of what to get him under the travel category unless he needs new luggage. Art and books, combine the two and get him a really nice art book?