I used a small clear bag on my last trip. Not to sound cheap but originally it was one of those bags that you get body wash, soap, lotions and such in and I kept it for taking to Disney. I only had sunscreen, extra film and some cereal bars to take in so I didn't need anything much bigger. Anyhow, I never had to open it. It made things quick and easy. I got several comments too - "makes my job easier, great idea ..." all along those lines.
That was so much easier than my son's first trip - he was still in diapers so we had to haul everything with us ... diapers, wipes, sippy cup, change of clothes...