Duaa- Before meals

Recite:
بِسْمِ اللَّهِ وَعَلَى بَرَكَةِ اللَّهِ
In the name of Allah and with the blessings of Allah I begin (eating)".

(Mustadrak)
On forgetting to recite Bismillah at the beginning, recite:
بِسْمِ اللَّهِ أَوَّلِهِ وَآخِرِهِ
"In the name of Allah in the beginning and end".
By not reciting Bismillah, Satan has an opportunity of partake in the food.

(Mishkat)