Something that needs to be said again... put your phone number and
maybe even a reward offer on the major pieces (nosecone and bodytube).
Marker, pen, sticky labels or engraving - who cares how, just do it!
These lists will grow as I discover new "necessities".
Things to check before you leave
The batteries in the launch controller.
Wind conditions/direction - unless your launch sites are perfectly square,
this may help decide which one is better.
Things to take to the field
Spare batteries for the launch controller.
Spare motor ignitors - get them with the same manufacturer name as your
motors.
CA glue (Krazy glue) - for emergency repairs.
Duct tape - this stuff is amazing.
Needlenose Pliers - for pulling stubborn objects from where they get jammed.
Utility knife - one of those snap-off, sliding blade type. or
Scissors (Don't run while holding them.)
If your launch site is covered in dead grass/weeds or the weather has been
dry for awhile.
Damp blanket - for under the launchpad.
Class 'A' fire extinguisher or a SuperSoaker watergun.
You will get very unpopular very quickly if you start a wildfire.
In a breeze, grass burns faster than you can walk.
Lastly, take kites with you just in case it's really too windy to launch.
No use wasting the day.