Babies don't really need a lot of stuff to be happy. They do delight in experiencing new shapes, textures, and colors, but there is plenty around the house that can just be given to baby outright to play with (wooden bowls, large wooden spools, etc.) and plenty of other things, that with a little transformation can become a dedicated plaything.
For this project, I started with a small paperboard gift box that I picked up at the craft store for under a dollar. I filled it with dried lentils. Not only do the lentils have a beautiful rainstick-like sound, they are also small enough that baby won't choke on them should the box accidentally come open. I then ran a line of hot glue around the inside of the lid and put the lid on the box, holding it in place for a moment or to so the glue could set.
I added his name to the lid with rub-on transfers that I had leftover from my scrapbooking days. The transfers claim to be non-toxic, but I decided to keep them to a minimum and to limit them to the top of the box, which I think he'll be less likely to put in his mouth, just in case.
You could do initials, a clever saying, or a small image. The possibilities are endless.