Apologies if I over-respond to this, but it's hard to talk without establishing that we're on the same wave length about a somewhat complicated topic ...

Bread bags are a cheap, temporary thing, but I often carry them as they're multi-purpose for me.

I don't carry a second set of footwear for camp or water crossings or whatever, and I don't use waterproof footwear, so the main use for me is for the evening/morning if my shoes are wet, I can have dry socks in camp and the breadbags keep the socks dry against wet shoes. Of course when I start hiking I put back on the damp socks (so as to keep the dry socks dry), but for in camp they're very nice. For that much use, breadbags are durable enough.

If I'm not carrying water resistant overmitten shells, breadbags can do that job in a pinch.

If there could be snow, cold weather, then --- also in a pinch --- they're sort of a "poor man's V.B. socks".

But there are actually vapor barrier socks designed to be just that, and from what you describe it could be that a pair of those would be worth while for you. The way you size them is based on what you want them to accomplish: are they to keep external water out and hence you wear wool socks inside them? Or are they to keep perspiration in?

The latter seems counter-intuitive, but the V.B. approach is to keep you warmer by eliminating heat transfer from moisture transport. I.e., similar to neoprene (but not that same!), you stay wet (in this case from your own perspiration) but it's the same liquid and you're able to warm it up. I'm not really expressing this well ...

Here, Skurka does a pretty good job:
http://andrewskurka.com/2011/vapor-barrier-liners-theory-application/

They can be purchased --- I actually own a pair, but in practice, I seldom hike where I think that I need them and so they mostly sit unused in my basement:
http://www.campsaver.com/rab-vapourbarriersocks-mens