Here is the basic list I give my students for painting outdoors. This isn't everything you need obviously and doesn't include stuff like brushes and paints, but it does tell you the extras and alternatives that will serve you well if you want to try painting outside.
If you want to sound posh then you can use the French term En Plein Air (literally 'in the fresh air')
MICHELE'S SUPER HELPFUL OUTDOOR PAINTING CHECKLIST:
Your usual equipment, plus:
Fold up chair, stool or blanket to sit on.
Drawing board/ masking tape/board clips in case it is windy.
Large plastic bottle full of painting water (don’t use river water, it is full of things that will eat your paper)
Small plastic palettes, plastic water containers/yogurt pots (don’t take glass into the countryside).
Kitchen paper/wet wipes/hand sanitiser. For when hand washing is not an option.
Sun-block (be careful not to get this on your paper via your forearms)
Waterproof hooded jacket in case of a run for the car, you won’t manage a brolly with all your stuff.
Extra lightweight clothing, cardigans, shawls etc will warm you if it is chilly and can be draped over shoulders or feet if you start to burn.
A painting or plastic storage box can double up as a foot rest or side table.
A wide brimmed hat is vital, painting in sunglasses is not recommended as it distorts the colours.
Food and drink.
Hayfever tablets/headache pills other medication as needed.
Insect repellent, bite cream.
A camera, in case you don’t get finished in time.
A fishing umbrella can help you stay out even if it’s raining (I’ll be in the car!)
RESPECTING NATURE... Tips to lessen your impact
Don't take glass into the countryside, if it breaks you won't be able to clean it up, risking animal/human feet not to mention grass fires.
Don't pour paint water away outdoors. Many paints (like Cadmiums) are toxic, at least allow it to go through the proper sewage system.
Leave animals alone. We have longhorn cattle where I live and every few years someone gets injured, almost always because they have been getting too close in order to take photos.
As my gran used to say leave it as you would like to find it. In otherwords don't leave anything behind and don't damage anything.
Here are some tips if this worries you!
There is safety in numbers... go with a friend or an art club.
You will meet the chap in the flat cap whose nephew was in the royal acadamy and who used to own a gallery and who knows everything about painting. Just smile and nod and keep working, eventually he will get bored and wander off if you don't engage too much.
Don't worry about critisism, it is very easy to critisise someone, much easier than making the effort to actually do something useful yourself.
Have a few deflective phases ready "I am just a beginner", "I just enjoy the process" "This is just a preliminary sketch" "I do it for the relaxation really".
Remember, most people are friendly and just interested in what is going on around them, relax and enjoy a chat whilst you work.