Create a "mobile studio" that I can take from place to place

I taped up one of my old portfolios and used it to transport:

Small pad
Large pad
Pencils + rubber
Script bundle

and carried a few more additional items in my rucksack.

It worked OK – I used the portfolio as a resting board, which finally persuaded the cat to stop fighting my sketchpad for my lap and just settle down beside me already – but I need to get a light included somehow.

• A3 resting board
• A3 paper
• A4 Clear board (for tracing)
• Craft light
• Pencils and erasers
• Pens and markers
• Inking equipment
• Specialist papers
• Script bundles

This all needs to be contained ideally within something I can carry in one hand, over a shoulder, or against my back. The A3 pannier strikes me as a possible candidate, or an A3 portfolio + bag, though I have a bad history with that, leaving it places and suchlike.