J.F.
Walmart for almost everything. But, you need to keep going back for the really cheap stuff because they keep running out. I got glue sticks for 10 cents, Crayola crayons (24) for 50 cents. Crayola markers for $1.97. Spiral notebooks for 17 cents.
Staples, Office Max and Office Depot are great for a few items, too. I got cheapy folders for 1 cent each, composition notebooks for $.25.
Buy extra while the prices are low. Great for around the home, and for when supplies run low at school.
(My oldest is going into K this year, too. Sniff!)
ETA: Dollar store for hand sanitizer, baggies, paper plates, etc.