Rite Aid and Walgreens often run Buy One, Get One Free on Ester C products.
When they do, make sure to have this $1 printable coupon on hand. You can use 2 of them on the BOGO sale, and the To Go packs are usually around $6. On a BOGO, that would bring 2 of the packs down to just $4 (or $2 each) with 2 of these printable coupons.