I haven't found any of the zip type bags can really stand up to much use; I also find they leak. I do have a "food-saver" type vacuum sealer that does work, it stays sealed and does not leak; the downside is once you open it, you can't reseal without the machine, and the plastic is tough enough that you probably need a knife to open it. If the kit is only for emergency use and you are usually have a small knife available, this may work. Another advantage is that the sealed bags tends to keep things from "walking away" and not being there when you need it.
Another alternative I like is screw top plastic jars. Less convenient to carry/pack, but they seal reliably, can be resealed, and when emptied can be used as a water container. I've found large ones at the local $ store, and of course recycle some of the smaller ones from our used grocery items. I use the zip type bags inside the plastic jar to help keep things organized.
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"Better is the enemy of good enough."