Target Stores' house brand "Up and Up" line includes an affordable SPF 100 sheer sunblock lotion sold in 3 oz tubes. I bought a bunch a year ago before a trip to Egypt, and it worked perfectly. The UPC code on it is 71661 82310. The tube's dimensions are such that it fits in your one quart Magic Blast Proof Safety Baggie™. The tube has a customer service phone number on it - 1-800-910-6874 - you could call if you have trouble finding it at your local store.

I've carried duplicates of the same item in my Magic Blast Proof Safety Baggie™; they are usually turned to face in different directions and/or obscured by other items. You can also ask other members of your party to carry some of your duplicates, in exchange for you doing the same favor for them.