pick a cloth hanger with a thin diameter (like one made of iron), hang it to a balanced tiny rope
at each end attach a rope with a plastic bottle cut in half
put the weighs in one and the stuff you r scaling in the other
theres the canadian loonie whih weights 7 grams as stated above and canadian 20 dollar bills is very close to a gram
if you want precision add of those thing to measure the leveling (water with a bubble you center)
edit : ive never used that method, i have a real scale but i dont use it as i never weigt stuff
(of course this require a perfect symetry)