There's a lot more discussion on the topic here:
http://forums.omnigroup.com/showthread.php?t=4374
But here's the way I do it:
1) Create a folder called "Templates" at the bottom of my list.
2) Inside that, create a "Traveling" project
3) Put that project "On Hold" in the inspector (This keeps its actions from showing up in views of things you 'ought' to be getting done.)
4) Start adding all those items to this project
5) At the bottom add an "Update Packing Template" item
6) When you need to go somewhere, select the "Traveling" project and copy and then paste it.
7) Now drag the copy to wherever it goes in your project hierarchy
8) Make the project "Active" and set a due date on it. Maybe even rename it to "Packing for Seattle visit" or wherever you're going.
9) Add anything specific to this trip such as "Umbrella" or "Mariners Tickets"
10) Do the stuff on the list
11) That last item on the list is to remind you to take the time to go back and update your template if anything has changed, like you got a cat and now you need to remember to arrange for its care before trips.