I've done a decent amount of traveling with a little one in tow, and surprise, surprise--when we're spending a lot of time in transit and away from home, bringing the right selection of books can make things easier.
My strategy is to aim for titles with lots of ways to read the same pages, but that don't add too much bulk to our luggage. Bringing some bedtime and naptime books can help maintain a familiar routine and coax sleep out of a kiddo in an unfamiliar place. And if you’re going to see family, it might be worth considering their tastes if you’re hoping to achieve some bonding or pass off some reading duties. An adult reader's excitement almost always translates into more interest from the listener.
For a younger baby (pre-movement), crinkle "books" (really toys, but with more to talk about in case you want to converse with baby) and song books are a good choice for multi-use entertainment.
If you're traveling by air, Planes (Amazon | Publisher) is a lift-the-flap that does a good job of depicting passenger aircraft and has a fun find-the-birdie element on every page.
Maisy's Plane (Amazon | Indiebound) is a way to start talking about flying with tiny people, and Maisy Goes on a Plane (Amazon | Indiebound) is an example story (in paperback) to walk kids through the experience ahead of time.
After we get past immediately relevant content, I'm looking for small size, durability, and long utility.
First 100 Words (Amazon | Indiebound) – lots of pictures to look at and discuss if you’re reading together, usually good for a few moments’ solo entertainment for the kiddo solo. No story.
Sniff/Lick/Munch (Amazon | Indiebound) – this Van Fleet trilogy focusing on the “other” senses has a lot of action in travel-size packages compared to his more famous large-format books. There is a rotten moment in Munch where the hippo that can’t stop talking has a prominent hairbow, the only piece of clothing in the book. Small hands will probably take these apart eventually, but they remain a pretty good bet for enclosed spaces.
Goodnight Moon (Amazon | Indiebound)– Board book version. An eternal choice for bedtime, this book also boasts long fame to endear it to those who don’t see little kids often and plenty of detailed illustrations and side attractions to discuss if you need to draw out storytime. Where’s the mouse? What’s in these other pictures?
Some Bugs (Amazon | Indiebound)– a small-format board book with lots of detail in the illustrations means lots of identifiable foods, objects, and animals not directly covered by the storyline in addition to the bug zoo on the last page. Where’s the watermelon? Can you find me a butterfly?
Peekaboo Kisses – (Amazon | Indiebound) Various animals with textured bellies hide behind liftable flaps. Tactile play, hide-and-seek, a mirror in the back, and the opportunity to go through animal noises mean one book starts a host of ever-popular toddler games. As lift-the-flap books go, it’s also pretty durable.
Siesta (Amazon | Indiebound) - plenty of early-word-recognition objects in a very detailed house, color games, two languages to play with, and it can also make a nice sleepytime book.
1001 Things to Spot in the Sea (Amazon | Indiebound). Toward two and above, look-and-find books can be a nicely time-consuming activity and engage more than one child if space allows. The genre has many small divisions of age appropriateness, but the younger end is rife with licensed characters. (We would probably pick Sesame Street-flavored poison but there are lots of options.) The Usborne series works well for pre-counters since there is plenty of color and action on each spread, but the pages are definitely rippable and the large format might make it a pain to carry.
Baby Babble (Amazon | Powell's) - For those below the look-and-find threshold, Tyvek books are a good option. Made of the same smooth, slippery not-quite-plastic stuff as a waterproof mailer, they are super lightweight, resistant to bending, and washable. I haven’t seen any that offer much by way of story, they’re very short, and I find them mostly not useful for solo entertainment, since the pages are hard for small hands to turn and the illustrations are an arty style my kid finds difficult to interpret. But as durable and portable as they are, there’s a lot to like. Baby Babble has a pretty good grasp on common first words and concepts of interest, so it makes a good place to start.
Sticker books are good for our behavioral emergencies. (Semi-relatedly, some very smart friends report that a roll of painter's or masking tape can help with entertainment and childproofing at your destination.)
Magazines – in a pinch, the in-flight magazine or a copy of whatever’s on sale at the gas station. Some of the pages will get shredded and eaten, but grownup stuff has a LOT of pages! You might even get to read some. Also makes fish puppets, paper hats, coloring surfaces, and airplanes.
A note on new vs. old: In my experience, novelty appeals to small kids, but not in the same way as for grownups. If you have time before your trip, try reading some new books you plan to take--but not too often, maybe just once or twice over a couple of days. If the book is a current favorite, you might want to hide it for a couple of days before you go. You want your travel library to feel fresh when you're on the road, but bringing only new books means you might be carrying them through the warming-up period where a baby doesn't "get" a book yet. Still, one or two brand-new ones can be great to bring out when everyone's patience is at a low.
Whatever else happens, traveling with a baby is rarely boring--and for almost any destination, it will be over in a matter of hours. You will make it. Good luck, don't forget the snacks, and bon voyage!