Anyway, I want to encourage you from a practical and enjoyment point of view, so what follows are some handy tips and thoughts. Remember, anyone can do this, you don't have to be an 'artist'.
1. Make sure you'll be warm (or cool enough) - think layers ie. cardigan, jacket etc. Wear comfy and practical shoes, after all, you never know where the muse might take you.
2. Bring a bag that can sling over your shoulder, is not too heavy, is waterproof (preferably wipeable if mud or cow dung gets onto it (yep, it's happened) and has ample space.
3. Of course, you need your journal/sketchbook and bulldog clips; they keep everything together. Small travel watercolour kit (including a palette), travel brush with inbuilt reservoir, paper towel, pencil, eraser, mini water-spray, pencil sharpener. Pop the smaller items into a make up bag or plastic sandwich bag (ziploc).
4. Don't forget your camera, batteries and don't do what I did, which was to run out of battery - gggrrr! Bring your 'regular' camera too. Cameras are great, not just for the 'Instagram moment' but for inspiration and possible further experimentation and reference for when you're at home.
5. A portable camping chair with it's own carry bag that can sling over your shoulder or, kneeling cushion (like you'd use for gardening) can be useful. Of course, you might not need these items but for me something to sit on is vital because otherwise my back starts playing up and/or my knees - (yep, midlife thing).
6. You need sustenance! Bring a snack or packed lunch and a drink for afterwards. This outdoor creativity thing is thirsty and hungry work! You might also need to bring insect spray, sunglasses, tissues, a map and sun protection. Oh, don't forget a paper bag for rubbish and/or bring it home with you -thinking leaving your environment as you found it.
7. Perhaps bring your journal (or write in your sketchbook) if you want to jot down a little of your process (ie. colours used) or record any other thoughts that are going through your mind once you've finished.
8. Tell someone where you'll be and a rough time you'll be back. I didn't do this and ended up calling my husband later on because I'd stopped off to a friend's house for a chat and lunch without pre-planning! He was 'getting concerned...', shall we say. ;)
You might not be happy with your work the first few times but that's no problem - it's a process. Make lots of thumbnail sketches and make a plan to visit again soon, so that you can 'firm up' your sketches and have another go.