Like the Boy Scout motto, " Be Prepared", you, as a plein air painter, must also remember to prepare wisely and to expect the unexpected! If you enjoy painting outdoors, you must think and plan ahead for your painting trip and carefully choose where you wish to paint and then check your surroundings.
Always research your location before you pack in order to understand what types of bugs or snakes live in the locale. Pack a small first aid kit with Benadryl for insect swelling and a sting stick for itchy bug bites. With the serious concerns of ticks, spray long pants and clothing with repellent. Consider wearing white long sleeves and white pants to easily see "hot spots" and carry a lint roller to remove the ticks from clothing. Leave infested areas immediately! Know what poison ivy looks like in its different stages and always avoid. Wear long pants around areas it is growing. Know that other people can get "contact" poison ivy from car seats, folding chairs, your clothing, or even a hand shake. (One time I borrowed a sun screen and spread poison ivy all over my arms because I touched the bottle, which had the poison on it!)
Think about the comfort of the clothing you'll need and wear layers for the potential cold or lighter clothing for warmer days. Be sure you have a hat that will keep you cool in the heat and protect you from sunburn, heat stroke or dehydration.
Most importantly, pay attention to the"false" sense of safety within us. Remember, that in our modern world of "Smart Phones", sometimes there is no reception or there are dead spots and no contact can be made for outside help. Know where you are going, take a buddy, tell a friend, and always have extra water! ~So many things to think of!