I do have a sweet tooth, but I control it. I saw both my parents die from obesity related diseases, and decided that I want to do my best to avoid that premature end.
As far as taking a cooler on the plane, all I take is one carry-on bag, so that is out of the question.
I made my living flying 2-3 times per week for about 5 years and never checked a bag.
For my mother-in-laws 80th birthday, we took her to Budapest - where her parents were born. We checked her luggage and went ahead and did ours while we were at it.
They lost them all. We got ours 2 days later, she never got hers. Even though we told her not to, she had some of her Parkinson's medication in the checked bag. Parkinson's people forget and when we asked her if she had her medicine with her, she said yes (but only 3 days worth). We called Delta and the Budapest airport every day.
On the way home, we stopped and checked the lost and found at the Budapest airport, and there it was.
Funny story after that. My DW and I already checked our bags so we checked mom's bag after we found it. Well this aroused the airport security. We were in line for boarding, and my DW was pulled aside and thoroughly searched, including her braided hair. I'm glad they were so thorough because even though we were innocent, the next person might not have been. Anyway, we have a good story to tell.
So for me it's one carry on. Travel shirts that dry out quickly, travel pants that do the same and have anti-pickpocket devices, essential personal items, and "survival food".
The Quest bars have more protein than fat, which of course isn't that good to keep you in ketosis, but that can be balanced with other things. Typically they are high fiber and low carb.
I used to do Atkins bars, but they have GMO soy in them, and after seeing a friend die from Agent Orange caused cancer, I'm not eating anything with Round-up residue on it if I can help it. But GMO is another thread.
On the other hand, if you are really concerned staying in ketosis, a jar of Nutiva Coconut Manna might do the trick for you. It's intense (and delicious), one tbsp is 100 calories, 9g fat and 1g protein - and of course the fat is that wonderful medium chain ketosis promoting coconut fat. I don't buy it anymore because for me, one jar could easily be a single serving
All I drink on the airplane is water, and I've been told that isn't safe because they refill the bottles. But I guess it's better than dehydration.
Bob