How much you take when you paint plein air depends on whether you're going to drive to a location in your car and work close to it, in which case you can take a lot, or whether you're going to walk to a location, in which case you need to be more selective in what you take. If you're going to walk any distance, consider a putting your art supplies into a backpack. Avoid overloading yourself. Start small and simple.
Checklist for Non-Painting Plein Air Essentials:
• It's easy to get caught up in what you're doing and end up sitting in the sun for an extended period, sometimes over the hottest part of the day, so remember to take some sunscreen and a sunhat.
• Dress in layers that you can easily take off as you get hot (and put on when it gets colder).
• If it's cold, take a windproof jacket as you may not be moving around much.
(Review: Scottevest Expedition Jacket)
• A pair of fingerless gloves helps keep your fingers warm while still giving good motion and grip.
• Something to sit on, such as a small cushion or an extra jumper. Consider taking a fold-up stool or chair if you know there's not going to be a convenient rock or wall to sit on and you don't want to sit on the ground.
• Some water to drink (don't rinse your brushes in it!) or a flask with coffee or tea (hot chocolate!) if it's cold.
• Wear neutral colored clothing (creams, beiges) rather than white which can reflect too much light onto your painting or bright colors which can reflect some of their color onto your painting.
• Insect repellent.
• A bag to put rubbish in, such as dirty pieces of paper towel.
• A large plastic bag can be useful as an emergency rainshield.
• A torch if you're going to be painting through sunset.
• A camera is useful for recording the scene in case you want to finish or work on the painting back in your studio.