Another thing that's nice about having NDs with you when you travel is they can help make a snapshot into a good shot. Last fall, the wife wanted to take a ride through Vermont. We stopped at the Bennington Battle Monument in the early afternoon, harsh light, not the setup for a great shot. While she went to the restroom, I stuck a Big Lee Stopper (10 stop) on the wide angle lens and pulled a 150 second shot off - the cloud blur made the photo and the other tourists disappeared over that exposure.
Going to FL next month, I've shot alot of sunsets on the beach before, but when the sun is near the horizon, that's the brightest part of the shot....so I just ordered a 3 stop reverse grad to try out. It's darkest in the center, you place that where the sun is and it should help balance the rest of the exposure.
Some people say you don't need grad filters anymore because you can do that in post, but in my experience, you can only go so far (depending on the body you are shooting) and to me, grads are very useful in addition to what you can do in post.