This book has been around for over 75 years and it's as much fun as ever! (and it has one of those colorways that makes me want to redecorate a room around it) I have fond memories of my brother stacking every hat and hat like thing up on his head, toddling around saying "caps for sale!". after we rediscovered it at the library the other week I had a gang of kids ranging from 1.5 to 4.5 begging me to read it over and over...and over.
There are so many cute caps for littles on Amazon that would tie in with this book. Unless you have a big budget and know the kid likes hats, you probably aren't going to get a whole stack of them, but all of the colors in the book are well represented. The peddlers own hat is the checkered one, so this one would be a great bet. Find the caps pictured here, (checked, gray, and red) and here (blue and brown).
~Like all links in this blog, the above are Amazon affiliate links~