Zippers and Snaps on travel bags are a problem; the problem is people forget to zip them or snap them shut. The safest travel bag is one that refuses to be used without being closed. Here are a couple photos of a great daypack, which truly protects the items in the bag.
This bag has a pull string, you can then use it as a backpack, however only when it is closed.
This is truly a great bag, I used to sell bags like this on my site, and one day I will again. I purchased another one today for 15 Quetzals to carry inside my computer bag and use for a grocery bag.
This design is one of the best selling school bags on the planet; I have seen this bag in most countries. However, I have used them for years as daypack. They do not use any room, and with a sewing machine, you could make a great one in an hour.
If you are truly a lightweight backpacker, this is the perfect daybag.
This is a great deal for 2 U.S. Dollars, wonder how much it cost in the USA or Europe?