I know it's still small but you can get more in the bag than you would get in a sheet of paper
Height 297mm (11.7 inches)
Width 210mm (8.27 inches)
Depth 210mm (8.27 inches)
Please note: this means the overall bag size. Bags that are half full and folded over to reduce their size will not be accepted.
I'm going to do what I used to do on planes, wear a heavy coat with lots of big pockets