While I've been painting for over 35 years, painting Plein Air (out of doors) is something I've only taken part in for the past couple of years. Some valuable things I've learned that make it easier for myself is to get my "stuff" ready and by the door the night before. Running around in the morning trying to remember everything and load up to get there on time, is no way to begin a Creative Plein Air Morning.
You want to be able to enjoy a cup of coffee too, before you start your day, so the less you have to do before setting out the better. Make a checklist, mental or otherwise, a checklist could save you some discomfort. My Checklist: Water, Hat, Garbage bag, Lip Balm, Light Over Shirt for a cover up, Paper Towels, Paint box with brushes and cleaner, Folding Chair, Folding easel, Prepared Canvas. Did I forget anything....my list is a Mental List :) Bug Spray!!