Thanks for your question.
Any prayer is only acceptable to God if it comes from the heart of one who worships Him in spririt and in truth. Desiring a pre-packaged prayer for any situation indicates that one is interested only in performing a religious ritual and not in communicating in any meaningful way with God.
When giving thanks for a meal. Speak from your heart a prayer of true thanksgiving. Don't reduce even this opportunity for prayer to the level of an empty ritual. Let your prayer be brief, focused, and sincere - the words of your heart not the empty formula of some stranger. That's how you offer a prayer for a meal or anything else.
I hope you have found this helpful.