We used actual fish crackers, which is lots of fun of course.
If you don’t want to use food items, there are fish to print and cut apart as an alternative.
Other pages have graphing and counting activities. Numbers of colors might be compared and contrasted, which is actually a form of addition and subtraction. Don’t tell the children, but they are going math if they realize 5 green fish is two more than 3 orange fish.
Children could also just color in the graphing spaces to show numbers in their bag. Candy might be used (have the children earned a special treat).
If you have other crackers or items on hand, you can write your own colors in the spaces along the bottom of one page. Perhaps you have colored buttons or counters. The next page would work with different items.