Here are some products that are (1) extremely useful, (2) may not be available from larger publishers, and (3) too much trouble to make yourself. I will be adding other such things as I can put them into production.
These cards allow Kindergarteners to tile anything from a 6-inch square to a 6-foot table. Later, as 2nd or 3rd Graders, they can use the same cards to create, identify, and compose fractions, and find equal fractions. I've used these cards in conjunction with paper folding to introduce fractions for almost 30 years. Now I bring them into enthusiastic K and Grade 1 students' classrooms to use as puzzle pieces.