I almost never leave the house without my knitting, be it for vacation or just a trip around town (you never know when you'll get stuck in traffic or a long line). I travel a bit for work and a bit for pleasure, so I feel like I have learned a few things about packing knitting projects for trips.
First off, I want to say that I always and completely overpack for travel. Pretty much you can probably cut whatever I suggest in half.
I am a super duper organized person, and I'm proud of that. Some of this may seem a little crazy, but this is what I do. Can you imagine being stuck in an airport with nothing to knit? My absolute worst nightmare. Like everyone else in the world, travel is super stressful for me. There are so many aspects you can't control or plan for, which causes me a lot of anxiety. I cope with that stress and anxiety by knitting. It's entertaining; I can do it forever, and it passes the time. It's the perfect thing to do while traveling.
I plan out at least three projects for any trip. I am not a multiple project knitter. I'm just not. So, I like to carry one with me and have two in my checked bags. If you do knit multiple things at once, you might want to bring all with you. I always figure, I'll finish one on the trip out, one while on vacation, and one on the way home. Of course, that has never happened. This rule does depend on the type of project. Three is my general rule for average length projects: hats, cowls, mittens... etc. If I'm knitting LGH inventory, I will bring more, because I knit that stuff quickly. If I was making a big wrap, I might just bring the one. No, that's a lie, I would never travel with less than two projects.
I pick my patterns and my yarn a couple of weeks before I leave so I have time get all the supplies I need. I get the yarn wound and pull all supplies I'll need for the project: needles, crochet hooks, cable needles.... etc. I print the patterns (in case I don't have access to the internet or power for my devices). I put one project in my project bag and pack it in my carry-on, and the other two projects in separate plastic bags. That way, I have a complete project in one spot. It keeps things simple and organized, and I don't have to get stressed searching through a bunch of supplies I don't need for what I do need. I love my project bag, but I am coveting a Fringe Supply Co. Field Bag. I just think they are cool and I like all the pockets on the inside. They are expensive though, but someday I'll treat myself, someday.
I have only had a problem with TSA once, and it was in Mexico, so I'm not sure if that's still considered TSA, but whatever the equivalent of Mexico's TSA is. I was stopped at security flying out of Mexico, they took my knitting project into a back room and then brought it back to me. I'm not sure what they did with it, but I was so scared. I knew I could get the project back, but I was nervous about not having anything to knit on the long flight from Cancun to Minneapolis.
Another time, I was sitting next to a woman on a flight, and she was very confrontational about me having knitting needles. She was SURE they were not allowed. She couldn't understand why I could bring knitting needles, but she couldn't bring a Diet Coke. I was friendly at first, but she would not let it go. Finally, I just told her, "I don't make the rules," and put on my headphones.
For the most part, people are always very interested in my knitting, "What are you making?", "My grandmother taught me to knit when I was seven," "how do you do that without looking." It's mostly nice and only sometimes annoying. :-)
Anyway, that's how I plan my knitting projects for a trip. I hope that's helpful!