Your backpack is sealed, and you're still naked, but I want to make 100% sure that you can't get to your clothes. There's still a chance you could pull the bag open a little bit, even with the zippers locked. It might be enough for you to slip a finger in there and pull out something to wear.
So take a zip-tie and loop it around the base of both zippers. It should be right at the bottom of the handles, where the handle meets the "zipper" part. Wrap it around and pull it as tight as you can. If you did this right, it should hold the "zipper" part of both zippers together so you can't open the bag even a tiny little bit. And it should have locked itself in place right at the base of the handles so you can't slide it up the handles and get any extra wiggle room. The backpack should be completely off-limits to you now.