I found this wonderful little travelling palette in the National Portrait Gallery shop - it's made by Koh-i-Noor - I thought the design was super. You would have to take your own brush & water, but it has it's own little mixing palette in the lid and one small water reservoir on each layer. Super compact design .... fits very nicely in my handbag!
This is the giant escalator at the National Portrait Gallery -
the Gallery is definitely worth a visit - wonderful stuff!
Not only modern portraits but rooms full of historic ones too, including my favourite Tudor/Elizabethan period.