If you like Post-It notes, look for them in Back To School flyers. You could find a deal to stock up on the 3 inch square notepads. The novelty shape notepads are seldom on sale so look for offers on them as well.
By chance, a box of letter size envelopes happened to be on sale when I decided to get a box to replenish my supply last week. You may find other incentives.
Some stores offer teen packs of personal care products-for a student going away to college or university, the packs could be welcome in the first month of school. The packs usually have a special price and once the stocks are gone, the packs are gone for the season.
On a quest for a 15cm plastic ruler? Well, it could be in a compass set. But sold singly? You'll be searching for a long time to find a retailer selling them singly. The metal 15cm rulers are sold at Walmart.