Don't forget big markers for the charts. Think about reflective vests for your gate steward. Include some nails, screws, duct tape, pliers, hammer, etc. Extra aluminum tent stakes always seem to come in handy. A good first aid kit for people and dogs is essential.
Someone always needs a bandaid, quick stop, etc.
Have a list of local vets, walk in clinics for people and hospitals which are easily accessible just in case. Small ice chests for each ring to hold water and drinks for your judges are very nice and much appreciated. You may also want to have Kleenex, hard candy, sun screen and insect repellant in a small basket for each judge as well. Golf tees and surveyors tape are handy to mark out waiting boxes, gamblers lines, flag off dangerous spots near the ring, etc. Extra sand bags usually come in handy too.