A lot of artists will admit to having an art supply addiction. Looking at most artists' studios it would probably appear as though they need some sort of intervention. Looks can be deceiving though. After much thought I realised I don't really have an art supply addiction, but more of a buyer's regret pile. You know how you can test drive a car? Some salesmen will even let you take it home for a couple of days so you get the idea of how great it would be to have it in your garage. Point is, you get to check out all of the features and see if the vehicle suits you. Not so much with art supplies. Yes, I have at least a half dozen travel (plein air) easels, but if I had been able to test drive one or two of them first I wouldn't have to keep shuffling them around my work space. So if you're in the same boat there's your defense.
Sadly it's not a solid defense. Even though I have travel palettes that work really well I still try to find, or build better ones. Perhaps there are just too many variables with travel and outdoor painting that there will never be a perfect solution. This first watercolour travel palette was inspired by one that John Preston bought on Etsy. It's made from a FlipNotes and empty makeup tins. The tins adhere to the case with magnetic tape and I used white enamel paint to make a mixing place.
This next one I made falls into one of those "variables" of travel. The airport security would have to have a pretty good sense of humour about this. The box is fun, but maybe not a great idea. If you want to test your luck get one for yourself over at BlueQ. This box is deep enough I used regular plastic half and full pans then painted the white enamel paint inside the lid for a mixing spot.
Since I was stinking up the studio with the white enamel paint I went ahead and fixed my old faithful. This is my original Schmincke watercolour palette that's been through the ringer a few times. It was rusty, stained and you can see where it's been dented. One coat of paint and it's like brand new. See, it's not always necessary to make a new one, but just maintain what you've got.
If you want to experiment and make your own travel palette your possibilities are pretty much endless. This person made one from a cheap eye shadow set. This site has a lot of variations as well. It seems as though you can make a travel palette out of just about anything. Just remember, unless you want a giant stash of travel palettes laying around, to consider your design and what you're using it for. They might be cute and fun but if they don't suit what you're using it for it will just be cute and collecting dust.
If you're not too busy building your own travel palette check out this nice write up on artist Heidi Annalise. She does tiny plein air oil paintings using an Altoid tin for a palette.