Buying the items separately might be good. You could find out from the parents and grandparents what he might already be receiving. Sometimes the godparents give the First Communion Rosary, the child’s first nice rosary. It varies so much with the individual family.
Back when dinosaurs roamed the Earth,

(i.e. 1969) I got my white dress, veil, white purse, and a little set in a clear vinyl bookcover kit which contained a missal and a pearl rosary, and my Brown Scapular. And a little gold-toned chalice pin.
For a boy, the kits are usually in black, and the rosary black or brown wood. Sometimes they wear a special necktie or armband.
I got my first real Bible for Confirmation, which back then was when I was 11. But nowadays a lot of people do get kids a Bible for First Communion.
Sometimes they get a picture Bible, which has enough text to read (more than a preschooler’s Bible, in other words) but isn’t the whole Bible, which may be beyond the reading level of a 7-year-old. And the picture Bible, of course, has illustrations.
Having the child’s name and date of the First Communion stamped on the Bible or written inside is a nice touch, too. Or in the Missal if you don’t get a Bible.