And also that every man should eat and drink... it is the gift of God. This enforces and intensifies the statement in the preceding verse; not only the power to "do good," but even to enjoy what comes in his way (see on Ecclesiastes 2:24), man must receive from God.
When we pray for our daily bread, we also ask for ability to take, assimilate, and profit by the supports and comforts afforded to us. "It" is better omitted, as "is the gift of God" forms the predicate of the sentence.
Ecclesiastes 11:1-10:17, "The gift of the Lord remaineth with the godly, and his favor bringeth prosperity for ever."