The pochade box
Pochade boxes are a great way of carrying everything you need for oil sketching in one wooden box. They come in various different styles but all have a compartment for storing your paints and brushes, a sliding or removable palette, and a lid that holds several painting boards. My pochade box (shown here) holds boards that are 6" x 8" (15cm x 20cm), but boxes come in several sizes larger than this as well.
Pochade boxes can be quite expensive, but I have found a good and very reasonably priced source in the UK at www.abbeyseasels.co.uk
You can buy a camera tripod mounting block to fix onto the bottom of the pochade from Ken Bromley Art Supplies in the UK. Go to www.artsupplies.co.uk and put KBCB in the search box.
Basic oil painting materials
You don't actually need much equipment for oil painting outdoors. I use a small selection of brushes ( a round, a flat and a fine point for details), and a cheap plastic palette knife for mixing colours on the palette and scraping it clean afterwards. I use a small dipper set that clips onto the palette and put just a few drops of low-odour thinners into one of the pots for brush cleaning.
I take just a few oil colours with me, a cool and a warm blue, a cool and a warm red, one yellow, white, yellow ochre and burnt sienna. With these I can mix any colour I need.
All these items fit neatly into the pochade box.
The only other essential items are either rags or kitchen roll for cleaning up and wiping your brushes as you go along (I much prefer kitchen roll as it is so easy to throw away paint covered pieces and tear off a few clean sheets during the painting process), and also a pack of baby wipes that are great for cleaning your hands and palette with afterwards. I don't know what they put into the wipes but they do remove paint very well.
Use masking tape to create a border
Here's a handy tip - put a strip of masking tape along each edge of your painting board and fold it over the back. When you have finished painting, remove the masking tape and you will have a picture that you can easily handle without getting covered in wet paint.
Pictures painted as outdoor sketches
Here are three of my outdoor oil sketches painted with the pochade box. They are all 6" x 8" and were painted in about an hour each. Note the white edge created by the masking tape, that makes them easy to handle as well as putting a nice border around them.