Yes, it is permissible to make duaa even if it is not one recorded in the Sunnah. The Prophet (pbuh) said, “Choose any supplication that you like and call upon Allah, the Mighty and Sublime, with it.” [Bukhari]
Sunnah acts of fasting continued:
Providing iftar for others who are fasting:
Even if just with a date or water; it is best to provide them with what fills them, if possible.
The Prophet (pbuh) said, “He who provides a fasting person something with which to break his fast will earn the same reward as the one who was observing the fast, without diminishing in any way the reward of the latter.” [Tirmidhi, al-Nasa’i, ibn Majah, ibn Haban]