When we're travelling I work on embroidery blocks that will be made into a quilt later. I try to collect fabrics that will go along with the blocks as we go.
I also have a hexagon project that I've carted around for years....it's not as "fun" so it's only brought out when I don't have time to prepare something else.
Hand appliqué is wonderful too, if you have a favourite holiday or season you could start on a little wallhanging for that.