Have Tupperware, Will Travel
It is funny how one thing can make your life so much easier...
For several years now I always take a medium sized tupperware container with me when we travel. Here is how I use it:
I fill it up with energy bars and comfort food. This way you don't have to worry about finding snacks for their daypacks during the first couple of days. (Read arriving in a small town late on Saturday when everything is closed and NOTHING is open on Sunday...) Comfort food is important, I have won Mother of the Year Award for pulling out Pop-Tarts in the middle of a 7-week overseas trip!
When staying in a hotel kids get really hungry in the morning and hate having to wait for everybody to get ready before going out for breakfast. Buy breakfast food the night before (like yoghurt, milk, cereal and fresh fruit), use some ice from the ice machine at the hotel and stick everything in the Tupperware. It will keep perfectly overnight and the kids can have something healthy first thing in the morning.
It is also the perfect place to soak the sleeve of the single white button-down shirt you brought your kid and now has a big ketchup stain on it!
As the snacks get eaten, I use the space to pack breakables or little knickknacks that we buy along the way. We have safely brought home glass fountain pens, balsamic glaze bottles, collections of magnets and ceramic figurines to name a few!
This is one of the few things I never travel without when we travel as a family!