So while taking an altoid tin with your diving wouldn't be the best idea, just splashing or raining will be perfectly fine.
Wow, we certainly have a different idea of "perfectly fine". Maybe a foot deep for an hour and it's got that much water in it? Betcha the cheapest zip-lock baggie wouldn't have that much moisture in it... Now, assuming we had our PSK goods in that tin: what would they be like the next time we opened the tin? Remember that this is a PSK, not a container for daily-use items. Could be a month, could be a few years, really no usual need to open except to upgrade/add. I guess the rule is to open a dunked Altoids PSK.
Just saying. I agree people may be over-reacting a bit. Cheap and handy vs "expensive" and built to do the required job. I used to use pipe tobacco tins and they sealed VERY tightly as found, you needed a coin to open them. Typically a bit of a gasket on the lid too.