I love this book (buy on Amazon). Actually, the main character Gilbert has a lot more books by Diane deGroat. It’s a nice book to show our students how kids like them celebrate Halloween in other country.
This book is not for early readers but I love the pictures. It’s a bit long, so you could summarize some parts.
In the official webpage, there are a couple of printables to use after reading like this one.(it’s the same as above)
Another activity after reading, it could be drawing a costume for the holiday. Probably, it’s a problematic idea because we should celebrate Halloween, but you could draw other costumes for Gilbert and make it a vocabulary class. I made a printable using the picture on this page.