I recently bought a really nice A4 kraft card sketchbook made by Seawhite here in the UK. I thought it would make me paint bigger, but the main reason was to have a single sketchbook that would allow me to use various opaque media like pastel, oil, acrylic, gouache and possibly charcoal and conte, and that I could take on holiday with me in a few weeks time. I've only managed to test oil and gouache but I really like the results so far.
For the first page shown here I used Caran D'Ache studio gouache cakes, These give similar coverage to normal tube based gouache but are in a convenient ready to use cake format so I could certainly use them on holiday.
For the second page, I used thinned oils at the top and normal Winsor & Newton designers' tube gouache at the bottom. I did a couple more samples with oils and they look really good, applied thicker than I did here, but unfortunately I cannot show those for reasons of plagiarism! If I do decide to use oils in this sketchbook, then I really ought to use a primer to stop the oil sinking but still keep the nice mid tone of the card and not loose the texture too much either.
I'm just trying to minimise what I take since boot space and weight is at a premium. I suppose I could take fewer clothes - I always take far more than I need!
PS Ralph Parker has some excellent tips and general thoughts on using gouache as an alternative to oils and acrylics and even advice on varnishing gouache paintings to give the effect of oils! But please leave me a comment before you zip off to Ralph's blog!