Dress according to the place you are headed to for a field trip. A field trip is not a place to show off your style quotient. Wear clothes that are functional and sensible. If you are expected to do a lot of walking, wear sturdy walking shoes that have soles with a good grip. If your park trip involves going into the surrounding wilderness, wear clothes that cover your body completely, such as jeans and T-shirt or a shirt with long sleeves. Even your socks should be all the way up to your ankles.
In case your park field trip involves staying overnight, carry a change of clothes, and preferably something warm, if you anticipate a dip in the temperature. Prepare for uninvited rain by carrying rain gear. Finally, bring a hat to keep the dust out of your locks, so that you don't end up spending hours in the shower to get the fields out of your hair.
Bringing along adequate food and water is the most important factor on a park field trip. If the field trip will be extremely long, and the weather a lot more than just sunny, it's best to stock up on water. In fact, consider carrying water in cans. A clever technique is to freeze two bottles of water overnight and carry them with two bottles of normal water. The frozen water will keep the normal water cool, and by the time you've finished the normal water, the frozen water will have melted for you to drink.
For food, forget sandwiches or burgers that will turn squishy in the bag. Instead, keep energy bars, dried fruit, cheese, and crackers. These things are high on nutritive value, but will not gather up too much space in your bag.
Depending on how long you are going to be out on your field trip, there are a few things you cannot afford to be without. These include sunscreen, insect repellent, first aid kit, sunglasses, and maps. Also carry your cell phone and a compass. Charge your phone's battery before the trip, and ensure that the compass is in proper working condition. If you are sure it will work, you can even carry along a GPS device if you plan to travel far from your vehicle. However, if you are headed to a remote and far-flung destination, chances are you may have to fall back on your old-fashioned compass for directions.