I can't say I recommend this but I suppose we've all been there...
get a pen where the ink can be removed - remove the ink and place a real thin piece of paper in there (maybe a mechanical pencil, it's not weird to disassemble that and less likely for ink blotch stains).
if your allowed gum and your careful unwrap the wrappers and scribble on the inside. Rewrap the candy so it looks untouched and place back in gum packet. Take a photo before unwrapping so you know how it meant to look. If the packet is wrapped in plastic then glad wrap and a hair dryer onto the plastic can make something look commercially rewrapped.
inside the lining of the pencil case. Or by sewing a brand label in on the inside you create a pocket for small paper. Aquire the brand fabric by cutting up another clothing item and undo the stitches using small scissors in the pencil case or a pencil sharper blade (this can be a bit difficult as you don't want to be wrestling with stitches in a pencil case in public)