Could someone explain to me how this works, and how do you know if you need a filler?

Have you read the FAQ section in the Walgreens forum?

You need a filler if you are using RRs and coupons to pay AND you don't have the same number of items as coupons and RRs. For example, you buy a razor for 8.99, use a $4 manu q and want to use a RR to pay less oop. You will need a filler - grab a pencil or some candy - and the RR will attach itself to it. Then, you are buying 2 items (the filler and the razor) and using 1 RR and 1 manu q.

sahm to Liliana and part-time tutor

Yep, just count up your items, then count your coupons plus any RR's you are using, and if those 2 #'s don't match you just need filler items until they do.

Co-Forum Leader for Rite Aid