When we took Dirty Delete for her first plane rides at about 15 months, I bought a bunch of cheap new toys and books and wrapped them up in wrapping paper before the flights. Each present probably occupied her attention for 15 minutes of more, and then we’d space letting her open a new toy with snacks, singing/playing finger games, playing with her old toys, reading books, etc…
Also, we took a 12 hour car ride with Dirty Delete when she was about a year, and we did the majority of the trip at night, which was absolute heaven. I put her in her pj’s and did her whole bedtime routine and then put her in her car seat instead of the her crib. On the return, we did it during the day, and while it was a lot more difficult, it was still doable. We tried to stop every hour to every 1.5 hours so Dirty Delete could get out and stretch her legs. Otherwise, we had a similar routine of giving her snacks, singing songs, reading books, and playing with her toys.
As far as activities to keep him entertained while you’re busy, Dirty Delete loves taking things out and putting them back in: crayons in/out of crayon boxes, Matchbox cars in/out of baskets or buckets, my credit cards in/out of my wallet, anything in/out of my purse, etc… The more challenging it is to get the item in/out, the better. Ummmm, she’s also gotten into stacking things lately, so her big Legos keep her attention for a while, as well as her set of wooden blocks. Oh, stickers are really big with her right now, too, and she’ll happily play with a page of stickers and a blank piece or paper for like 15 minutes.
Finally, I’m not sure how you feel about screen time at this age, but I have this free Droid app on my phone called Zoodles. It has a bunch of age-appropriate YouTube videos that Dirty Delete loves. Most of the videos are 1-2 minutes long, and it’s things like clips from Sesame Street, shapes/colors/letters introductions, videos of animals, animations of children’s songs, etc… As our last resort when Dirty Delete really doesn’t want to sit still in a place where she can’t get up and run around, we’ll let her watch a video or two on my phone, and that keeps her happy for a few more minutes.
ETA: I feel like I should add that we rarely ever leave Dirty Delete completely on her own. If I’m doing something in the kitchen, she comes with me and does activities in her highchair. If I need to shower, she comes in the shower with me and plays with her bath toys. Imo, toddlers can’t be trusted to be on their own for more than a minute or two, lol, so we encourage independent play in an area we can still watch her, instead of leaving her alone to her own devices.