Dedication to training is a great and necessary part of bodybuilding, but everyone needs a break sometimes. In fact, taking an occasional break is good to allow your body time to grow and recuperate. Often, when you come back form a break, you'll find that you will shock your muscles back into a growth phase. But one thing that is important is maintaining your nutrition, and especially for hard gainers, keeping your caloric intake up.
But how can you do that when you're on vacation? If you are actually taking a trip, it may be hard to do this. Your food intake me be sporadic, and you might have to just eat what you can get. The key to overcoming this problem is planning ahead. For example, recently I took a trip to Australia. I went from the US, through Europe and across Asia all in one trip. Almost thirty hours on a plane, and with layovers included it was forty-eight hours without a real meal. When they served those in-flight meals, I ate everything, right down to the cream for the coffee. I also carried several meal replacement bars in my carry-on bag, and ate those on the flight. (Remember if you're traveling internationally to declare any food in your bag; I learned customs isn't too happy if you forget to do that.) Consequently, I was able to keep from getting hungry, and by eating big while I was actually on vacation, I did not lose too much hard-earned weight.
When you're on your trip, eating out is probably going to be the main source of your food. Just remember, try to eat clean, but most importantly, keep your caloric intake up. If you're a hardgainer, that hard-earned mass will start dropping quickly if you're meals drop off. Explain to the people you are traveling with that you need to eat every three to four hours and plan your trip accordingly. Planning ahead is the key.
What if you're doing something that leaves you even more isolated from food, such as camping or backpacking? The high carbohydrate dehydrated food that most campers pack is good for replacing energy stores, but it does not have anywhere near the protein that a bodybuilder needs. Solution? The meal replacement bars help, but you're going to need more than just that. Some good things to take are cans of tuna and jars of peanut butter. Both are excellent sources of protein, and the peanut butter is calorie dense and contains a lot of good fats. Both those things will add weight that you have to carry with you, but remember you're a bodybuilder; you can handle a little extra weight. We don't eat like normal people, and we have to compensate for our increased nutritional needs.
My personal favorite meal replacement bars are Sportpharma's ProMax Bars and Met-Rx's Nutritional Food Bars. Both of these bars contain good sources of protein and plenty of carbs without too much sugar. There are plenty of good brands of bars out there, just be on the look out for bars with a lot of saturated fat or sugar. Other good foods you can carry are, like I've mentioned, cans of tuna (they even have vacuum-sealed packages of tuna now), natural peanut butter, fresh roasted nuts (not the canned kind dripping in oil though), dried beef, and canned salmon. You don't have to worry about keeping these things fresh and they can go anywhere with you.
As far as training goes, remember your body needs a periodic break. If however, you are going to be away from the weights for more than a month, you might want to do some bodyweight resistance exercises to try to maintain strength. Push-ups, crunches, and pull-ups are your best bets for this. No matter where you are, you should be able to find a place and some time to fit in some exercises. As far as specific routines, I would do somewhere in the range of roughly 50 reps all three movements, roughly four times a week. You'll have to go with what feels right for you, but doing these movements will help you maintain strength. You can even find some kind of weight to put on your back when doing push-ups or pull-ups to add resistance. Be creative.
Overall though, have fun on your trip. Everyone needs to get away for a little while, and your body needs a break sometimes too. As bodybuilders, we push our bodies to the max to get everything we can out of them. As long as you maintain your nutrition as best you can, a little time away will do your mind and body good.