Here is a popular bag I came up with using some small plastic animals we already had and some strips of card stock. Make squares to place the animals on, labeled with numbers to practice counting. Ben is really getting into counting right now (he can count to 11 already!!) so this is a great activity for him. Meanwhile, Molly needs to work on writing and recognizing her numbers so it's important for her to practice while looking at them written down. I also included some easy math problems, which can be added to and upgraded as my kids get older.
I also included three pieces of card stock with habitats on them so my kids can sort the animals by where they live. This is Molly's favorite part. I only used animals we already had, so that limited my habitats, but if I bought more animals we could also use a Farm or Pet Store for example. Once your child gets older, you could use this idea with more specific habitats (fresh water stream, lake, desert, rainforest, savannah, etc).
Another really popular activity I found on Pinterest that my kids love is a simple color-sorting activity. I found some great plastic gems at a dollar store in four different colors - a buck per package. Then I cut out four rectangles of felt in matching colors. Ben does a really good job sorting these gems - it is such good practice for him! Any craft gem or stone or small toy will work... you just need several of each color!