Though I have a core curricula I use for each of my students...I love supplementing with extra materials. I scour the internet for free printables and activity ideas for all ages.
For example, I add nature journaling, using the Handbook of Nature Study to my first graders science agenda (read more about it here). I also use these no-nonsense science workbooks, Focus on Science. The pages make great work samples for our learning record meetings.
These workbooks are black and white, with simple, easy to understand, age appropriate reading and in book activities that match the state standards for that grade.
For my older students, like my 8th grader...I look for supplementary materials that correspond with the lesson in her Oak Meadow Science book. This week was a lesson on solids and liquids. Perfect timing as I had just come across this free printable activity and worksheet. We didn't have all the supplies on hand but we had most. We improvised! :-)
I find most of my supplementary resources online in the form of free printables and worksheets (Pinterest is your friend!) but I have also found items at Dollar Tree, believe it or not, in their educational/school section.