Prophet (SAW)'s Prayers

At meal times when visiting someone
اللَّهُمَّ أَطْعِمْ مَنْ أَطْعَمَنِي وَاسْقِ مَنْ سَقَانِي
"O Allah, feed him for he has fed me and quench his thirst for he has quenched my thirst".

Alternate dua
أَكَلَ طَعَامَكُمُ الْأَبْرَارُ وَصَلَّتْ عَلَيْكُمُ الْمَلَائِكَةَ وَأَفْطَرَ عِنْدَكُمُ الصَّائِمُونَ
"(May) the righteous partake of your food and the angels of mercy descend upon you and those who are fasting break their fast with you.

(Hisnul Hasin)
Also recite the above dua which praises Allah and thanks Him.