Packing these 10 items (whether on a day trip or overnight) is the best practice for being a prepared and responsible public lands user.
Navigation: map, compass, GPS device, or satellite messenger. Be sure to bring a printed map in addition to an electronic device - don't rely on your phone for navigation in emergencies!
Headlamp: with extra batteries
Sun protection: sunglasses, hat, sun-protective clothes, and sunscreen
Firt Aid: including foot care and insect repellent (as needed)
Knife: or multi-tool plus a gear repair kit
Fire: matches, lighter, tinder and/or stove
Shelter: should be carried at all times (could be an emergency tarp, space blanket, or light emergency bivy)
Extra food: beyond the minimum expectation (carry at least one extra day's worth of food that doesn't require cooking)
Extra water: beyond the minimum expectation - bring a filter or water purification tablets as well
Extra clothing: bring rain gear and extra non-cotton layers
In addition to the 10 Essentials, here is a basic gear list for an overnight trip:
Tent
Sleeping bag
Sleeping pad
Cooking stove
Cooking pot/Utensils
Water filter
Rain Gear / Layers
Headlamp
P Cord
Compass + map
Bugnet
First Aid Kit
Hand Tool
Poop kit
Heavy duty and small trash bags
Plan ahead to ensure you have the proper equipment to accomplish your work. Tool kits for your planned activity will be provided by the USFS but before going out in the field, check to make sure you have the following:
Trailhead signs/posters
Scantron permits
Pencils/pens
T50 stapler + staples
Hammer
Measuring Tape
Crescent Wrench
Pliers
Socket wrench + kit
Lag bolts + washers
Screwdriver + screws
Drill + extra battery
Drill bits
Drill sockets
Shovel
Lag bolts
Washers
Socket wrench + appropriate size bits
Hammer
Chisel
Garbage bags (1 heavy duty, 1+ small)
Latex & work gloves
Shovel