I used Reading Street up until this year, and I never did centers. I printed packets of worksheets for kids to work on independently while I met with groups. (But honestly, I never felt great about so much teaching with worksheets and I'm not sorry we switched curriculums.

)
I got a lot of materials/worksheets off a website called waltke's web. I deleted all my RS bookmarks, but you should be able to find it if you Google. Actually, just Google Reading Street second grade or something, because they're are several sites with tons of resources.