What do you use for your "pouch or sub-bag"? Rigid containers? Ziplock bags? Vacuum sealed bags?

I have a couple of things that I like to organize in modules too. And the biggest headache for me is finding the proper sized and shaped container to hold each module. I vary all over the place for these containers. Sometimes a small divided fishing lure box, sometimes a 35mm film canister (I sure wish you could still get the old metal ones!), sometimes a vacuum sealed bag, sometimes a simple rubber band bundling things together, sometimes a soft margarine tub, sometimes a stuff sack, etc. Any ideas folks have for what to use as internal containers would be appreciated. Any shape, any size - I have other things besides emergency kits that I like to modularize. Another problem I have when using all these various containers is that it's not immediately obvious if the thing I'm holding is a module, or something that fell out of a module, as some of the containers are difficult to label in a stand-out/obvious way.

I've thought about overwrapping every module in a vacuum sealed bag. That would make them obvious (and waterproof). Except once you cut open that vacuum bag, the contents are free to fall out. Maybe this isn't a big deal for emergency kits that you carry often, but rarely use.