Even if I forget to do it on the day, I try to add it in at a later date. It's not that hard to remember roughly what you ate. Even if you don't get it exactly right, you must have a pretty good idea of what you had so put in everything you can remember. The longer you're doing this, the better you'll get at judging weights and measures, even if you don't get to weigh/measure them at the time.
Whatever you do will be insignificant, but it is very important that you do it -
| current weight: 169.0