Trabasack is a bag with a built in lap tray. The bag has a firm top and removable bean bag and comes in 2 different sizes and designs. There is the smaller Trabasack Mini and the larger Trabasack Curve. There's a choice of surfaces and straps available.
The smaller Mini is suitable documents up to A4 in size or use a laptop bag for laptops and netbooks up to 13" screen size. The zips are large and can be locked with a small padlock.