Can a yid be yotzei mantanos leveyonim and shalach munos at one time to an oni if he has nothing else to give?
One should not fulfill both mitzvos together.
This question is widely discussed among different authorities.
Based on the Gemara in Megillah (7b), the Turei Even writes that one cannot give one item of food and use it for both mitzvos. This ruling emerges from certain versions of the Gemara’s text (which is disputed).
However, Shut Daas Sofer (130) writes that one can fulfill two mitzvos at once, and having given food to a poor person, one would only have to give charity to one other poor person to complete the mitzvah of matanos la-evyonim. Shut Kesav Sofer (139) notes that this will incur a problem of “performing mitzvos in bundles,” but the Sedei Chemed (Aleph, Kelalim 95) writes that this is not a problem.
The Chemsad Moshe (Perlmutter, 14) writes that this can only be done if the poor person has other (poor) members of his household.