What is the halacha what does the shlach monos have to contain?
It should contain two types of foods (not clothing or utensils), even if the foods are the same bracha. The two types have to be foods that are ready to eat, but not raw meat etc. that have to still be cooked.
It is preferable that the two types be something that would be considered a prominent gift to the person receiving it. Therefore giving a candy and a cookie to a child might be considered a prominent gift for him, but to an adult it wouldn’t, therefore when sending to an adult the two items should be more prominent. ( Note: This is only a preference, after the person has already given one shalach manos, the rest of the people that he is giving to don’t need this preference)
Shulchan Aruch 695-4, Taz 4, M:B 19, 20, Biur Halacha ibid D:H Chayiv