I'm guessing from the other posters that you're flying? Nursing on take off and landing, checking with the airline for information on infant seat regulations and pre boarding, bringing a sling, packing an extra top for you and an outfit for the little one, having more diapers and wipes than you think you'll need, carrying a clean blanket for nursing and sleeping and swaddling, and checking everything you can so that you're hands are free...these are all essential tips. But don't forget a small bag for yourself with a mama pad or two (in case walking between terminals and the stress of travel bring back some post-partum flow), some nursing pads if you use them, a BIG bottle of water and some nutritious snacks for yourself, and a book or tape you can use with one hand for after the little one falls asleep.
Since I don't see in your original post that you're flying though, let me suggest some ideas for driving (dd and I went on several road trips when she was in the 3-4 months range, spending between 5 and 10 hours in a car at a time). Since you'll have a bit more room in a car, you don't have to worry as much about packing light. Remember diapers, wipes, and nursing pads (if you're using disposables or will be using disposables for the trip) can be bought at your destination so don't pack more than you need for a day or two. Pack a larger "snack" bag for the trip and include water, fruit, sandwiches, and whatever else you might want to have close to hand. Bring a couple of blankets in case you need to change your little one by the side of the road or at a rest stop with no changing tables. And I'd recommend taking the time to change the little one as soon as they're wet even if that means a roadside stop since they'll be much happier as a result!
Also, it takes a little bending and flexing, but you can nurse a little one in their car seat while still wearing your own seatbelt. As I said, it's a bit tricky, but with some bending and stretching you can do it and it makes a trip much faster if you can nurse your little one as soon as they show a need rather than waiting till you reach a rest area or pull off to nurse.
At the hotel...bring some waterproof pads or blankets you sleep on at home and put them on the hotel bed if you co-sleep. This way the bed will feel and smell familiar to your little one and you wont have to worry about the bed getting wet, or ickiness from the bed getting on your little one. If you use a crib of some sort either bring it from home (like a pp mentioned) or bring the sheets and blanket for those familiar scents and cleanliness.
The front desk people can be a huge help...ask them about where to buy diapers/wipes or if you can use the hotel washing service for cleaning cloth diapers/infant clothes (but remember they'll be using a stronger detergent than you might at home, so also ask for directions to a nearby laundromat or ask if you could hand wash items in your room but use the hotel dryers). Also ask for directions to a nearby food store since it's always cheaper to buy some snacks and mini-meals to have on hand. If your room doesn't have a fridge, ask the desk for one. It's worth a small fee for the length of time you'll be there, but they'll probably provide it for free. Buy some yogurt cups, soup cups and instant oatmeal packs that can be made up using hot water from the coffee pot (most rooms now have coffee pots...just run it empty for hot water), and some sandwich fixings. While at the store pick up some small garbage bags to hold dirty diapers or dirty clothes waiting to be laundered. The more dirty items can be wrapped up, the nicer the air in your room will stay and the happier the cleaning staff will be!
A few large blankets or play mats will give you something to lay your dc down on for play time or to change their diaper.
Bring things to entertain yourself during your little one's nap times. A sling for walking the halls and area around the hotel is good too. Ask the front desk about family friendly events or places of interest near the hotel. You may not feel up to a huge outing on your own with the little one, but a nearby library or children's museum would be a good place to meet local parents who might have ideas of things to do.
Enjoy the trip and remember to bring a camera to prove you and your family really did make it through the adventure!