Never weighed food. I base whos getting feed what size rodent by how big the snake is.
Everyone of my snakes has its own cage card. The card records when it ate, defecated, weights, shed, and refusals. I keep good records because i like to get weights after one snake defecates to give a more accurate (empty) weight. I feel everyone should keep cage card for their snakes(even if its just feeding/refusals/weights) just for the simple fact that if your ball python starts a fasting period, unless you mark it as refusals, 6 weeks could really be 10+ weeks with no food, and unless you know weights you dont know how much the snake has truly lost.
but i guess i just like having all my records in order. i also take photcopies of all papers that come with a animal, and put the originals in my safe, and photocopies go into the snakes folder.