If you have older kids, let them know in advance how much they have to spend. This way, they can pick which items they want to “splurge” on and which ones they don’t. They may want to spend a lot on a nice notebook but stick to the cheaper pencils and pens.
Many stores already have back-to-school deals on certain items. Quickly glance through some deal sites and store ads to see which items are on sale and stock up on the basics- pens, notebooks, glue sticks, etc.
Different stores- physical and online have different things on sale at different times. Usually, office supply stores are the most expensive place to get the supplies on your school supplies checklist, and big box stores, dollar stores, or online stores are cheaper.